2788 + Interview Questions in GRAVITATION IN GENERAL AWARENESS Page 20 InterviewSolution

951.	The minimum velocity of projection of a body to send it to infinity from the surface of a planet is `(1)/(sqrt(6))` times that is required from the surface of the earth. The radius of the planet is `(1)/(36)` times the radius of the earth. The planet is surrounded by an atmosphere which contains monoatomic innert gas `(gamma = 5//3)` of constant density up to a height h(`h lt lt` radius of the planet). Find the velocity of sound on the surface of the planet.
Answer» Escape velocity from the surface of the planet `v_(p)=sqrt(2g_(p)R_(p))` Given `v_(p)=(v_(e ))/(sqrt(6)) = sqrt((2g_(e )R_(e ))/(6))` `sqrt((g_(e )R_(e ))/(3)) = sqrt(2g_(p)R_(e )//36) rArr g_(p) =6g_(e )` Pressure exerted by the atmospheric column of height h on the surface of the planet `P = rho g_(P) h` Using equation of state `P = (rho RT)/(M)` Hence speed of the sound `v = sqrt((yRT)/(M)) = sqrt(yg_(p)h) = sqrt(6y g_(e )h) = sqrt(10 g_(e )h)`

Discussion

952.	A body is released at a distance far away from the surface of the earth. Calculate its speed when it is near the surface of earth. Given `g=9.8ms^(-2)` radius of earth `R=6.37xx10^(6)m`
Answer» Conservation of energy implies `0+0=1/2mv^(2)-(GMm)/R` `v=sqrt((2GM)/R)=sqrt((2(R^(2)g))/R)` `=sqrt(2Rg)~~11.2xx10^(3)ms^(-1)`

Discussion

953.	Weightlessness in space: Space travellers as well as objects in the spacecraft appear to be floating. Why does this happen? Though the spacecradft is at a height from the surface of the earth the value of g there is not zero. In the space station the value of g is only 11% less than its value on the surface of the earth. Thus, the height of a spacecraft is not the reason for their weightlessness. Their weightlessness is caused by their being in the state of free fall. Though the spacecraft is not falling on the earth because of its velocity along the orbit, the only force acting on it is the gravitational force of the earth and therefore it is in a free fall state. As the velocity of free fall does not depend on the properties of an object, the velocity of free falls is the same for the spacecraft, the travellers and the objects in the craft. Thus, if a traveller releases an object from her hand, it will remain stationary with respect to her and will appear to be weightless. Why is weightlessness caused in a spacecraft?
Answer» The weightlessness is caused by them being in a state of free fall.

Discussion

954.	Weightlessness in space: Space travellers as well as objects in the spacecraft appear to be floating. Why does this happen? Though the spacecradft is at a height from the surface of the earth the value of g there is not zero. In the space station the value of g is only 11% less than its value on the surface of the earth. Thus, the height of a spacecraft is not the reason for their weightlessness. Their weightlessness is caused by their being in the state of free fall. Though the spacecraft is not falling on the earth because of its velocity along the orbit, the only force acting on it is the gravitational force of the earth and therefore it is in a free fall state. As the velocity of free fall does not depend on the properties of an object, the velocity of free falls is the same for the spacecraft, the travellers and the objects in the craft. Thus, if a traveller releases an object from her hand, it will remain stationary with respect to her and will appear to be weightless. If a traveller releases an object from her hand in the spacecraft, what will happen?
Answer» The object will remain stationary with respect to her, because, the velocity of free fall is the same for the sapcecraft, traveller and objects in the craft.

Discussion

955.	If the potential energy of a body at a height h from the surface of the earth is `(mgR)/(2)`, thenA. h = 2RB. `h = (R )/(2)`C. `h = (R )/(3)`D. h = R
Answer» Correct Answer - D `P.E.=-(GMm)/(R+h)=(-gR^(2)m)/(R+h)` In magnitude, `(gR^(2)m)/(R+h)=(1)/(2)mgR` `therefore R + h=2R " " therefore h = R`

Discussion

956.	Assertion : If earth were a hollow sphere, gravitational field intensity at any point inside the earth would be zero. Reason : Net force on a body inside the sphere is zero.A. If both assertion and reason are true and the reason is the correct explanation of the assertion.B. If both assertion and reason are true but reason is not the correct explanation of the assertion.C. If assertion is true but reason is false.D. If the assertion and reason both are false.
Answer» Correct Answer - A

Discussion

957.	Two satellites A and B go round a planet in circular orbit of radii 4 R and R respectively. If the speed of satellite A is 4 v, then the speed fo satellite B will beA. 12 vB. 8 vC. 4 vD. v
Answer» Correct Answer - b `V_(1) prop (1)/(sqrt(r_(1)))and V_(2)prop (1)/(sqrt(r_(2)))` `(v_(2))/(v_(1))=sqrt((r_(2))/(r_(1)))`

Discussion

958.	The orbital speed for an earth satellite near the surface of the earth is `7km//sec`. If the radius of the orbit is `4` times the radius of the earth, the orbital speed would beA. 3.5 km/sB. 7 km/sC. 72 km/sD. 14 km/s
Answer» Correct Answer - a Orbital velocity `=sqrt((GM)/(R))=7"km/s"` `v=sqrt((GM)/(4R))" "therefore(7)/(v)=(sqrt(GM//R))/(sqrt(GM//4R))=(2)/(1)` `therefore" "v=(7)/(2)=3.5"km/s"`

Discussion

959.	Distance of moon from the centre of earth is ………………….. cm. A) 3.844 × 1010 B) 3.844 × 106 C) 3.844 × 105 D) 3.844 × 104
Answer» A) 3.844 × 10¹⁰

Discussion

960.	Fc \(\cfrac{mv^2}R\) is given. Here what is v ? A) speed of a particle B) weight of a particle C) velocity of a particle D) momentum of a particle
Answer» C) velocity of a particle

Discussion

961.	set Aset Bv = u + atas = ut + \(\cfrac{1}2\) at2h = \(\cfrac{gt^2}2\)v2 – u2 = 2asbSet A are the equations of uniform accelerated motion. Set B are the equations of a free fall body. Then a & b areA) v = -gt, v2 = -2gh B) v = gt, v2 = 2.gh C) v = g – t, v2 – g2 = 2h D) A or B
Answer» B) v = gt, v² = 2.gh

Discussion

962.	If 1 kg body weights 1.2 N and 2 kg body weights 2.4 N on a planet. Then the acceleration due to gravity on that planet is A) 9.8 m/s2 B) 2 m/s2 C) 2.1 m/s D) 1.2 m/s2
Answer» Correct option is D) 1.2 m/s²

Discussion

963.	When an object is dropped from a height, it accelerates and falls down. Name the force which accelerates the object.
Answer» The force that accelerates the object is gravitational force of the earth.

Discussion

964.	When an object is dropped from a height, it accelerates and falls down. Name the force which accelerates the object.
Answer» Gravitational force of the earth.

Discussion

965.	When an object is dropped from a height, it accelerates and falls down. Name the force which accelerates the object.
Answer» Correct Answer - Gravitational force ( of earth)

Discussion

966.	Give the formula for the gravitational force F between two bodies of masses M and m kept at a distance d from each other.
Answer» Correct Answer - `F=Gxx(Mxxm)/(d^(2))`

Discussion

967.	Mass of an object is 10 kg. what is its weight on earth ?
Answer» Correct Answer - 19.6 N

Discussion

968.	The value of acceleration due to gravity of earth :A. is the same on equator and polesB. is the least on polesC. is the least on equatorD. increase from pole to equator
Answer» Correct Answer - c

Discussion

969.	Calculate the gravitational force on a body of mass 1 kg lying on the aurface of earth. Given mass of earth. Given mass of earth is `6xx10^(24)` kg and radius of earth is 6400 km.
Answer» Here, `m_(1)=1kg, m_(2)=6xx10^(24)kg` `d=6400 km =6.4xx10^(6)m, F = ?` `F = (Gm_(1)m_(2))/(d^(2)) =(6.67 xx 10^(-11)xx1xx6 xx 10^(24))/((6.4 xx10^(6))^(2)) =9.8N`

Discussion

970.	The mass of the Earth is `6xx10^(24)kg`. The distance between the Earth and the sun is `1.5xx10^(11)m`. If the gravitational force between the two is `3.5xx10^(22)N` what is the mass of the sun? `G=6.7xx10^(-11) Nm^(2)//kg^(2)`
Answer» Given `m_(1)=6xx10^(24)kg` `r=1.5xx10^(11)m` `F=3.5x10^(22)N` `G=6.7xx10^(-1)Nm^(2)//kg^(2)` To find `: m_(2)=?` Formula `F=(Gm_(1)m_(2))/(r^(2))` Solution: `(Fr^(2))/(Gm_(1))=m_(2)` `m_(2)=(3.5xx10^(22)xx(1.5xx10^(11))^(2))/(6.7x10^(-11)xx6xx10^(24))` `=(7.875xx10^(44))/(40.2xx10^(13))` `=7.875/40xx10^(31)` ltbr. `=0.196xx10^(31)kg` `=1.96xx10^(30)kg` The mass of the Sun is `1.96xx10^(30)kg`

Discussion

971.	What is the magnitude of the gravitational force between the Earth and a 1kg object on its surface ? (Mass of the earth is `6xx10^(24)` kg and radius of the Earth is `6.4xx10^(6) m)`.
Answer» The magnitude of gravitational force is calculated by using the formula : `F=Gxx(m_(1)xxm_(2))/r^(2)` Now Gravitational constant `G=6.7xx10^(-11)Nm^(2)//Kg^(2)` Mass of earth `m_(1)=6xx10^(24)kg` Mass of object `m_(2)=1 kg ` And , Distance between center r=Radius of earth of earth and object `=6.4 xx 10^(6) m` Now,Putting these values in the above formula ,we get ` F=(6.7xx10^(-11)xx6xx10^(24)xx1)/((6.4 xx10^(6))^(2)` or F= 9.8 N Thus the magnitude of gravitational force between the earth and a 1 kg objective on its surface is 9.8 newtons.

Discussion

972.	Write true or false for the following statements:Acceleration due to gravity is expressed asg =G\(\frac{M}{R^2}\)Where, symbols have their usual meanings.
Answer» True Explanation: The acceleration produced in a freely falling body by the gravitational pull of the earth is called the acceleration due to gravitation. We know that, Force = Mass × Acceleration F = m × a a = \(\frac{F}{m}\)............1 Where, F is the force on the object of mass m dropped from a distance r from the centre of earth of mass M. So, force exerted by the earth on the object is F = G\(\frac{M\times m}{r^2}\).............2 M = Mass of Earth m = mass of object r = distance of object from centre of earth Now, from equation 1 and 2, a =G\(\frac{M\times m}{r^2\times m}\) a =G\(\frac{M}{r^2}\) Now, from above, a = g = Acceleration due to gravity Hence, g = G\(\frac{M}{r^2}\)

972.

Write true or false for the following statements:Acceleration due to gravity is expressed asg =G\(\frac{M}{R^2}\)Where, symbols have their usual meanings.

Answer»

True

Explanation: The acceleration produced in a freely falling body by the gravitational pull of the earth is called the acceleration due to gravitation.

We know that,

Force = Mass × Acceleration

F = m × a

a = \(\frac{F}{m}\)............1

Where, F is the force on the object of mass m dropped from a distance r from the centre of earth of mass M.

So, force exerted by the earth on the object is

F = G\(\frac{M\times m}{r^2}\).............2

M = Mass of Earth

m = mass of object

r = distance of object from centre of earth

Now, from equation 1 and 2,

a =G\(\frac{M\times m}{r^2\times m}\)

a =G\(\frac{M}{r^2}\)

Now, from above,

a = g = Acceleration due to gravity

Hence,

g = G\(\frac{M}{r^2}\)

Discussion

973.	Assessment (A) : The net force which change only the direction of the velocity of a body is called centripetal force. Reason (R) : Centripetal force exists only in uniform circular motion. A) A and R are trueB) A and R are false C) A is true but R is false D) A is false but R is true
Answer» A) A and R are true

Discussion

974.	Which of the following statement is true ? Statement 1 : Velocity and acceleration of a body in a uniform circular motion are perpendicular to each other. Statement 2 : The direction of the acceleration of a body in uniform circular motion is always towards its centre. A) 1 B) 2 C) 1 and 2 D) None
Answer» Correct option is C) 1 and 2

Discussion

975.	For a freely falling body, a = ………………. A) – g B) + g2C) + g3D) + g
Answer» Correct option is D) + g

Discussion

976.	A body weighs more at the pole than at the equator, Why?
Answer» Because the polar radius is lesser, the body weighs more at pole than at the equator.

Discussion

977.	Write an expression for the mass of the earth.
Answer» An expression for the mass of the earth is gR_e²/G.

Discussion

978.	What are the dimension of gravitational constant G?
Answer» The dimension of gravitational constant G is: [M^-1 L³ T^-2]

978.

What are the dimension of gravitational constant G?

Answer»

The dimension of gravitational constant G is:

[M^-1 L³ T^-2]

Discussion

979.	Write the formula for the gravitational potential energy of mass 'm' at a finite distance 'r' in the gravitational field of mass M.
Answer» The formula for the gravitational potential energy of mass 'm' at a finite distance 'r' in the gravitational field of mass M is -GMm/r.

Discussion

980.	What is the value of G?
Answer» It is 6.67 x 10^-11 Nm² kg^-2

Discussion

981.	What is the force of attraction between the earth and a body of mass 1 kg?
Answer» The force of attraction between the earth and a body is 9.8.

Discussion

982.	Suppose the radius of earth is half of its present value (Mass remaining unchanged). The value of g at a height equal to the final radius is `10 x m//s^(2)`. Find the value of x.
Answer» Correct Answer - 1

Discussion

983.	What is the unit of intensity of gravitational field?
Answer» The unit of intensity of gravitational field is: N kg^-2

983.

What is the unit of intensity of gravitational field?

Answer»

The unit of intensity of gravitational field is:

N kg^-2

Discussion

984.	Match the column : A particle at a distance r from the centre of a uniform spherical planet of mass M radius `R(lt r)` has a velocity v magnitude of which is given in column I. Match trajectory from column II about possible nature of orbit. `{:(,"Column I",,"Column II"),((A),0lt V lt sqrt((GM)/(r )),(P),"Straight line"),((B),sqrt((GM)/(r )),(Q),"Circle"),((C ),sqrt((2GM)/(r )),(R ),"Parabola"),((D),v gt sqrt((2GM)/(r )),(S ),"Ellipse"):}`
Answer» Correct Answer - A::B::C::D

Discussion

985.	What is the value of 'g' and 'G' at the centre of the earth?
Answer» g is zero while G = 6.67 x 10^-11 Nm² kg^-2

Discussion

986.	A planet moves in elliptical around sun, at one of focal points. Match the following, for different parameters related to the planet during the motion `{:(,"Column I",,"Column II"),((A),"Kinetic energy",(p),"Maximum at perigee"),((B),"Gravitational potential energy",(q),"Minimum at perigee"),((C ),"Linear momentum",(r ),"Maximum at apogee"),((D),"Area swept per second radius",(s),"Minimum at apogee"):}`
Answer» Correct Answer - A::B::C::D

Discussion

987.	Match the following `{:(,"Column I",,"Column II"),((A),"Maximum and minimum gravitational potential",(p),"Upon surface, upon centre and infinity"),(,"of a solid sphere of mass",,),((B),"Minmum and maximum gravitational field intensity",(q),"Upon infinity, upon centre"),(,"(magnitude) of a ring mass",,),((C ),"Maximum and minimum (magnitude) of gravitational",(r),"Upon centre, upon axis at distance " (R )/(sqrt(2))" from centre"),(,"field of a mass spherical shell",,),((D),"Minimum and maximum gravitational field",(s),"Upon centre, surface"),(,"(magnitude) of solid sphere",,),(,,(t),"Continuous"):}`
Answer» Correct Answer - A::B::C::D

Discussion

988.	What is the effect of altitude on the acceleration due to gravity?
Answer» Acceleration due to gravity (g) decreases with altitude.

Discussion

989.	As orbital radius r of a satellite is increased, state which of the following quantities will increase and which will decrease ? (i) Orbital speed (ii) Time period (iii) Frequence (iv) Angular speed (v) Kinetic energy (vi) Potential energy (vii) Toyal mechanical energy .
Answer» (i) Orbital speed`nu_(0) = sqrt ((GM)/(r))` or `nu_(0) prop (1)/(sqrt(r))` Therfore, orbital speed will decrease. (ii) `T = 2pi sqrt(r^(3)/(gR^(2)))` or `T prop r^(3//(2)` (iii) Frequency , `f = (1)/(T)` Time period is increasing . So frequency will decrease. (iv) Angular speed `omega = (2pi)/(T)` or `omega prop (1)/(T)` Time period is increasing . Hence , angular speed will decrease . (v) Kinetic energy, `K = (GMm)/(2r)` or `K prop (1)/(r)` Terfore, kinetic energy will decrease . (vi) Potential energy ` U = (GMm)/(r)` or `U prop -(1)/(r)` Therfore, potential energy will increase . (vii) Total mechanical energy, `E = -(GMm)/(2r)` or `E prop -(1)/(r)` So, mechanical energy will also increase .

Discussion

990.	What is meant by weightlessness?
Answer» A sense of apparent loss in weight in situations like when falling freely under gravity, when bodies are in zero gravity region etc., is called weightlessness.

Discussion

991.	What is the value of gravitational potential energy at infinity?
Answer» The value of gravitational potential energy at infinity is zero

Discussion

992.	A geostationary satellite is orbiting the earth at a height of `6R` above the surface oof earth where R is the radius of the earth .The time period of another satellite at a distance of `3.5R` from the centre of the earth is ….. hours.
Answer» `T prop r^((3)/(2))` or `:. (T_(2))/(T_(1)) = (r_(2)/(r_(1)))^(3/2)` or `T _(2) = (r_(2)/(r_(1)))^(3/2)T_(1)` `T_(2) = ((3.5R)/(7R))^(3/2) (24)h = 8.48h` `(T_(1) = 24 h` for geostationary satellite)

Discussion

993.	The force due to gravity upon an object is known as its ………… A) frictional force B) gravitational force C) weight force D) both B & C
Answer» D) both B & C

Discussion

994.	Statement-1: The acceleration of a particle near the earth surface differs slightly from the gravitational acceleration Statement-2: The earth is not a uniform sphere and because the earth rotates.A. Statement-1 is true, statement-2 is true: Statement-2 is a correct explanation for statement-1B. Statement-1 is true, Statement-2 is true, Statement-2 is not a correct explanation for Statement-1C. Statement-1 is true, Statement-2 is false.D. Statement-1 is false, Statement-2 is true.
Answer» Correct Answer - A

Discussion

995.	The escape velocity v of a body depends on 1. the acceleration due to gravity ‘g’ and 2. the radius of planet ‘R’Find the relation between them using dimension analysis.
Answer» We know that, Escape velocity = V = [LT^-1 ] Acceleration due to gravity = g = [LT^-2] and Radius = R = [L] ⇒ Let V = kg^aR^b ⇒ [LT^-1] = [L^aT^-2a] [L^b] a + b = 1 and -2a = -1 ⇒ a = \(\frac {1}{2}\) and b =\(\frac {1}{2}\) So, V = k \(\sqrt {Rg.}\)

995.

The escape velocity v of a body depends on 1. the acceleration due to gravity ‘g’ and 2. the radius of planet ‘R’Find the relation between them using dimension analysis.

Answer»

We know that,

Escape velocity = V = [LT^-1 ]

Acceleration due to gravity = g = [LT^-2]

and Radius = R = [L]

⇒ Let V = kg^aR^b

⇒ [LT^-1] = [L^aT^-2a] [L^b]

a + b = 1 and -2a = -1

⇒ a = \(\frac {1}{2}\) and b =\(\frac {1}{2}\)

So, V = k \(\sqrt {Rg.}\)

Discussion

996.	Two particles A and B of masses 1 kg and 2 kg respectively are kept 1 m apart and are released to move under mutual attraction. Find The speed A when that of B is 3.6 cm/hr. What is the separation between the particles at this instant?
Answer» The linear momentum of the pair A+B is zero initially. As only mutual attractiois taken into account, which is interN/Al when A+B is taken as the system the linear momentum wil remain zero. The particles move in opposite directions. If the speed of A is v when the speed of B is 3.6 cm/hour `=10^-5ms^-2`. (1kg)v=(2kg)(10^-5ms^2-1)` v=2xx10^-5ms^-1` The potential energy of the pair is `-(Gm_Am_B)/R` with usual symbols. Initial potential energy `=-(6.67xx10^-1N-m^2/kg^2xx2kgxx1kg)/1m` `=13.34xx10^-11J` if the separstion at the given instant is d using conservation of energy `-13.34xx10^-11J+0` `=-(13.34xx10^-11J-m)/d+1/2(2kg)(10^-5ms^-1)^2` `+1/2(1kg)(2xx10^-5ms^-1)^2` Solving this d=0.31m

Discussion

997.	Class 9 Science MCQ Questions of Gravitation with Answers?
Answer» It’s a crucial chapter, therefore, you’ll need to develop in-depth learning of the Class 9 Science MCQ Questions of Gravitation with Answers. Students often confuse several terms included during this chapter. These MCQ Questions will act as a self-assessment for you once you’ve got studied the whole chapter. To help you in exams your understanding, here could be a list of MCQ questions for class 9 Science. confirm you have got skilled these chapters earlier, and only then do you begin with this examination. Practice MCQ Questions for class 9 Chapter-Wise 1. Two objects of different masses falling freely near the surface of the moon would (a) have same velocities at any instant (b) have different acceleration (c) experience forces of the same magnitude (d) undergo a change in their inertia 2. A boy is whirling a stone tied to a string in a horizontal circular path. If the string breaks, the stone (a) will continue to move in the circular path (b) will move along a straight line towards the center of the circular path (c) will move along a straight line tangential to the circular path (d) will move along a straight line perpendicular to the circular path away from the boy 3. The atmosphere is held to the Earth by (a) gravity (b) wind (c) clouds (d) Earth’s magnetic field 4. An object weighs 10 N in air. When immersed fully in water, it weighs only 8 N. The weight of the liquid displaced by the object will be (a) 2 N (b) 8 N (c) 10 N (d) 12 N 5. The acceleration due to gravity on the Earth depends upon the (a) mass of the body (b) mass of the Earth (c) shape and size of the body (d) volume of the body 6. .......of a body is the quantity of matter contained in it. (a) mass (b) weight (c) volume (d) none of these 7. The earth and the moon are attracted to each other by gravitational force. The earth attracts the moon with a force that is: (a) More than that exerted by the moon (b) Same as that exerted by the moon (c) Less than that exerted by the moon (d) Not related to that exerted by the moon 8. An apple and a stone dropped from a certain height accelerates (a) equally (b) differently (c) depending on density (d) depends on the position of the Sun 9. The pressure exerted by man on earth is minimum when he (a) sits (b) stands on one foot (c) stands on both feet (d) lies on ground 10. When a body floats in a liquid, its apparent weight is always (a) less than the weight of the body (b) more than the weight of the body (c) equal to the weight of the body (d) zero 11. School bags have a broader base to reduce (a) pressure (b) weight (c) air resistance (d) normal reaction 12. The weight of an object is least in some region of the earth. What will be the color of bears found in that region? (a) black (b) white (c) blue (d) brown 13. SI Unit of pressure is (a) Pascal (b) Newton (c) m/s (d) Dyne 14. Density of a substance is defined as mass per unit …………….. (a) weight (b) volume (c) time (d) pressure 15. The relative density of a substance is the ratio of its density to that of (a) air (b) water (c) vacuum (d) none of these 16. Weight of an object on the surface of the moon is (a) 1/6 that on the surface of the earth (b) 1/5 that on the surface of the earth (c) 1/3 that on the surface of the earth (d) 1/2 that on the surface of the earth 17. The atmosphere is held to the Earth by (a) gravity (b) wind (c) clouds (d) Earth’s magnetic field 18. For a given applied thrust, the pressure exerted on a surface by a sharp pin is (a) more than the pressure exerted by a blunt pin (b) less than the pressure exerted by a blunt pin (c) equal to the pressure exerted by a blunt pin (d) either less or equal to the pressure exerted by a blunt pin 19. Earth moves in a circular motion around the Sun because of ........... force, (a) frictional (b) static (c) applied (d) gravitational 20. What is buoyant force- (a) An upward force on an object immersed in a liquid (b) Partially downward force (c) A downward force on an object immersed in a liquid (d) None of the above See Answer below> Answer: 1. Answer : (a) have same velocities at any instant Explanation: Objects of different masses falling freely near the surface of the moon would have the same velocities at any instant because they will have the same acceleration due to gravity. 2. Answer : (c) will move along a straight line tangential to the circular path Explanation: The moment the string breaks the centripetal force acting towards the center ceases and hence no force acts on the system. So by Newton's first law of motion, the stone will continue in a straight line and will fly off along the tangent of the circular path. 3. Answer : (a) gravity Explanation: The atmosphere is held around the Earth by gravity. 4. Answer : (a) 2 N Explanation: F = 10- 8 = 2N 5. Answer : (b) mass of the Earth Explanation: The acceleration due to gravity depends upon the radius of the earth, a mass of the earth, and on a constant having unit Nm²/kg². 6. Answer : (a) mass Explanation: The mass of a body is the quantity of matter it contains. 7. Answer : (b) Same as that exerted by the moon Explanation: According to the universal law of gravitation, two objects attract each other with equal force but in opposite directions. Therefore, the earth attracts the moon with the same force as the moon attracts the earth. 8. Answer : (a) equally Explanation: The free fall of both objects will be the same. Both of them will fall due to the gravitational pull of the earth. 9. Answer : (d) lies on the ground Explanation: The pressure is inversely proportional to the area. As the area is maximum while lying down( unless the feet are incredibly large), therefore pressure will be minimum. 10. Answer : (d) zero Explanation: The apparent weight of a floating object is zero. 11. Answer : (a) pressure Explanation: School bags are provided with broad straps to increase the surface area in contact with the shoulders and reduce pressure on the shoulders. If thin straps would be used, then the surface area in contact with the shoulders would decrease which will lead to an increase in pressure on the shoulders. 12.Answer : (b) white Explanation: Acceleration due to gravity is less in the case of poles and colour of bears found in these regions are white, called as a polar bear. 13. Answer : (a) Pascal Explanation: The SI unit for pressure is the pascal (Pa), equal to one newton per square metre (N/m², or kg·m^-1·s⁻²). 14. Answer : (b) volume Explanation: Density, the mass of a unit volume of a material substance. The formula for density is d = M/V, 15. Answer : (b) water Explanation: The relative density of a substance is the ratio of its density to the density of water. A substance with a relative density less than 1 will float in water. For example, an ice cube, with a relative density of about 0.91, will float. A substance with a relative density greater than 1 will sink. 16. Answer : (a) 1/6 that on the surface of the earth Explanation: The moon's gravitation force is determined by the mass and the size of the moon. Hence, the weight of an object on the moon is 1/6th its weight on the earth. 17. Answer : (a) gravity Explanation: The atmosphere is held around the Earth by gravity. 18. Answer : (a) more than the pressure exerted by a blunt pin. Explanation: For a given applied thrust, pressure exerted on a surface by a sharp pin is. more than the pressure exerted by a blunt pin. 19. Answer : (d) gravitational Explanation: The earth moves around the sun because of the gravitational force of the sun on the earth. This force acts along the radius of the orbit of the earth towards ( or focus) its center. 20. Answer : (a) An upward force on an object immersed in a liquid Explanation: Buoyant force is a force acting on an object opposite to gravity by fluid which is being submerged partially or completely in a fluid. It opposes the weight of an object. The buoyant force is given by volume displaced by an object into a density of fluid into gravitational acceleration. Click here to Know more MCQ Questions for class 9 Gravitation

997.

Class 9 Science MCQ Questions of Gravitation with Answers?

Answer»

It’s a crucial chapter, therefore, you’ll need to develop in-depth learning of the Class 9 Science MCQ Questions of Gravitation with Answers. Students often confuse several terms included during this chapter. These MCQ Questions will act as a self-assessment for you once you’ve got studied the whole chapter.

To help you in exams your understanding, here could be a list of MCQ questions for class 9 Science. confirm you have got skilled these chapters earlier, and only then do you begin with this examination.

Practice MCQ Questions for class 9 Chapter-Wise

1. Two objects of different masses falling freely near the surface of the moon would

(a) have same velocities at any instant
(b) have different acceleration
(c) experience forces of the same magnitude
(d) undergo a change in their inertia

2. A boy is whirling a stone tied to a string in a horizontal circular path. If the string breaks, the stone

(a) will continue to move in the circular path
(b) will move along a straight line towards the center of the circular path
(c) will move along a straight line tangential to the circular path
(d) will move along a straight line perpendicular to the circular path away from the boy

3. The atmosphere is held to the Earth by

(a) gravity
(b) wind
(c) clouds
(d) Earth’s magnetic field

4. An object weighs 10 N in air. When immersed fully in water, it weighs only 8 N. The weight of the liquid displaced by the object will be

(a) 2 N
(b) 8 N
(c) 10 N
(d) 12 N

5. The acceleration due to gravity on the Earth depends upon the

(a) mass of the body
(b) mass of the Earth
(c) shape and size of the body
(d) volume of the body

6. .......of a body is the quantity of matter contained in it.

(a) mass
(b) weight
(c) volume
(d) none of these

7. The earth and the moon are attracted to each other by gravitational force. The earth attracts the moon with a force that is:

(a) More than that exerted by the moon
(b) Same as that exerted by the moon
(c) Less than that exerted by the moon
(d) Not related to that exerted by the moon

8. An apple and a stone dropped from a certain height accelerates

(a) equally
(b) differently
(c) depending on density
(d) depends on the position of the Sun

9. The pressure exerted by man on earth is minimum when he

(a) sits
(b) stands on one foot
(c) stands on both feet
(d) lies on ground

10. When a body floats in a liquid, its apparent weight is always

(a) less than the weight of the body
(b) more than the weight of the body
(c) equal to the weight of the body
(d) zero

11. School bags have a broader base to reduce

(a) pressure
(b) weight
(c) air resistance
(d) normal reaction

12. The weight of an object is least in some region of the earth. What will be the color of bears found in that region?

(a) black
(b) white
(c) blue
(d) brown

13. SI Unit of pressure is

(a) Pascal
(b) Newton
(c) m/s
(d) Dyne

14. Density of a substance is defined as mass per unit ……………..

(a) weight
(b) volume
(c) time
(d) pressure

15. The relative density of a substance is the ratio of its density to that of

(a) air
(b) water
(c) vacuum
(d) none of these

16. Weight of an object on the surface of the moon is

(a) 1/6 that on the surface of the earth
(b) 1/5 that on the surface of the earth
(c) 1/3 that on the surface of the earth
(d) 1/2 that on the surface of the earth

17. The atmosphere is held to the Earth by

(a) gravity
(b) wind
(c) clouds
(d) Earth’s magnetic field

18. For a given applied thrust, the pressure exerted on a surface by a sharp pin is

(a) more than the pressure exerted by a blunt pin
(b) less than the pressure exerted by a blunt pin
(c) equal to the pressure exerted by a blunt pin
(d) either less or equal to the pressure exerted by a blunt pin

19. Earth moves in a circular motion around the Sun because of ........... force,

(a) frictional
(b) static
(c) applied
(d) gravitational

20. What is buoyant force-

(a) An upward force on an object immersed in a liquid
(b) Partially downward force
(c) A downward force on an object immersed in a liquid
(d) None of the above

See Answer below>

Answer:

1. Answer : (a) have same velocities at any instant

Explanation: Objects of different masses falling freely near the surface of the moon would have the same velocities at any instant because they will have the same acceleration due to gravity.

2. Answer : (c) will move along a straight line tangential to the circular path

Explanation: The moment the string breaks the centripetal force acting towards the center ceases and hence no force acts on the system. So by Newton's first law of motion, the stone will continue in a straight line and will fly off along the tangent of the circular path.

3. Answer : (a) gravity

Explanation: The atmosphere is held around the Earth by gravity.

4. Answer : (a) 2 N

Explanation: F = 10- 8

= 2N

5. Answer : (b) mass of the Earth

Explanation: The acceleration due to gravity depends upon the radius of the earth, a mass of the earth, and on a constant having unit Nm²/kg².

6. Answer : (a) mass

Explanation: The mass of a body is the quantity of matter it contains.

7. Answer : (b) Same as that exerted by the moon

Explanation: According to the universal law of gravitation, two objects attract each other with equal force but in opposite directions. Therefore, the earth attracts the moon with the same force as the moon attracts the earth.

8. Answer : (a) equally

Explanation: The free fall of both objects will be the same. Both of them will fall due to the gravitational pull of the earth.

9. Answer : (d) lies on the ground

Explanation: The pressure is inversely proportional to the area. As the area is maximum while lying down( unless the feet are incredibly large), therefore pressure will be minimum.

10. Answer : (d) zero

Explanation: The apparent weight of a floating object is zero.

11. Answer : (a) pressure

Explanation: School bags are provided with broad straps to increase the surface area in contact with the shoulders and reduce pressure on the shoulders. If thin straps would be used, then the surface area in contact with the shoulders would decrease which will lead to an increase in pressure on the shoulders.

12.Answer : (b) white

Explanation: Acceleration due to gravity is less in the case of poles and colour of bears found in these regions are white, called as a polar bear.

13. Answer : (a) Pascal

Explanation: The SI unit for pressure is the pascal (Pa), equal to one newton per square metre (N/m², or kg·m^-1·s⁻²).

14. Answer : (b) volume

Explanation: Density, the mass of a unit volume of a material substance. The formula for density is

d = M/V,

15. Answer : (b) water

Explanation: The relative density of a substance is the ratio of its density to the density of water. A substance with a relative density less than 1 will float in water. For example, an ice cube, with a relative density of about 0.91, will float. A substance with a relative density greater than 1 will sink.

16. Answer : (a) 1/6 that on the surface of the earth

Explanation: The moon's gravitation force is determined by the mass and the size of the moon. Hence, the weight of an object on the moon is 1/6th its weight on the earth.

17. Answer : (a) gravity

Explanation: The atmosphere is held around the Earth by gravity.

18. Answer : (a) more than the pressure exerted by a blunt pin.

Explanation: For a given applied thrust, pressure exerted on a surface by a sharp pin is. more than the pressure exerted by a blunt pin.

19. Answer : (d) gravitational

Explanation: The earth moves around the sun because of the gravitational force of the sun on the earth. This force acts along the radius of the orbit of the earth towards ( or focus) its center.

20. Answer : (a) An upward force on an object immersed in a liquid

Explanation: Buoyant force is a force acting on an object opposite to gravity by fluid which is being submerged partially or completely in a fluid. It opposes the weight of an object. The buoyant force is given by volume displaced by an object into a density of fluid into gravitational acceleration.

Click here to Know more MCQ Questions for class 9 Gravitation

Discussion

998.	Assertion: if an earth satellite moves to a lower orbit, there is some dissipation of energy but the satellite speed increases. Reason: The speed of satellite is a constant quantity.A. If both the assertion and reason are true and reason is a true explantion of the assertion.B. If both the assertion and reason are true but the reason is not true the correct explantion of the assertion.C. If the assertion is true but reason falseD. If both the assertion and reason are false.
Answer» Correct Answer - C Due to resistance force fo atmosphere, the satellite revolving around the earth losses kinetic energy. Therefore, in a particular orbit the gravitational attraction of earth on satellite becomes greater than that required for cicular orbit there. therefore, satellite moves down to a lower orbit. In the lower orbit as the potential energy `(U=-GMm//r)` becomes more negative, hence kinetic energy `(E_(K)=GMm//2r)` increases, and hence speed of satellite increases.

Discussion

999.	Assertion: Geostationary satellite appear fixed from any point on earth. Reason: The time period of geostationary satellite is `24` hrsA. If both the assertion and reason are true and reason is a true explantion of the assertion.B. If both the assertion and reason are true but the reason is not true the correct explantion of the assertion.C. If the assertion is true but reason falseD. If both the assertion and reason are false.
Answer» Correct Answer - A Geostationary satellites orbit around the earth in the equatorial plane with time periode of `24`hrs. since the earth rotates with the same periode, the satellite would appear fixed from any point on earth.

Discussion

1000.	Assertion: The time period of geostationary satellite is `24` hrs. Reason: Geostationary satellite must have the same time period as the time taken by the earth to complete on revolution about its axis.A. If both the assertion and reason are true and reason is a true explantion of the assertion.B. If both the assertion and reason are true but the reason is not true the correct explantion of the assertion.C. If the assertion is true but reason falseD. If both the assertion and reason are false.
Answer» Correct Answer - B As the geostationary satellite is established in an orbit in the plane of the equator at a particular place, so it move in the same sense as the earth and hence its time period of revolution is equal to `24` hrs, which is equal to time period of revolution of earth about its axis.

Discussion

Explore topic-wise InterviewSolutions in .

A body is released at a distance far away from the surface of the earth. Calculate its speed when it is near the surface of earth. Given `g=9.8ms^(-2)` radius of earth `R=6.37xx10^(6)m`

If the potential energy of a body at a height h from the surface of the earth is `(mgR)/(2)`, thenA. h = 2RB. `h = (R )/(2)`C. `h = (R )/(3)`D. h = R

Two satellites A and B go round a planet in circular orbit of radii 4 R and R respectively. If the speed of satellite A is 4 v, then the speed fo satellite B will beA. 12 vB. 8 vC. 4 vD. v

The orbital speed for an earth satellite near the surface of the earth is `7km//sec`. If the radius of the orbit is `4` times the radius of the earth, the orbital speed would beA. 3.5 km/sB. 7 km/sC. 72 km/sD. 14 km/s

Distance of moon from the centre of earth is ………………….. cm. A) 3.844 × 1010 B) 3.844 × 106 C) 3.844 × 105 D) 3.844 × 104

Fc \(\cfrac{mv^2}R\) is given. Here what is v ? A) speed of a particle B) weight of a particle C) velocity of a particle D) momentum of a particle

set Aset Bv = u + atas = ut + \(\cfrac{1}2\) at2h = \(\cfrac{gt^2}2\)v2 – u2 = 2asbSet A are the equations of uniform accelerated motion. Set B are the equations of a free fall body. Then a &amp; b areA) v = -gt, v2 = -2gh B) v = gt, v2 = 2.gh C) v = g – t, v2 – g2 = 2h D) A or B

If 1 kg body weights 1.2 N and 2 kg body weights 2.4 N on a planet. Then the acceleration due to gravity on that planet is A) 9.8 m/s2 B) 2 m/s2 C) 2.1 m/s D) 1.2 m/s2

When an object is dropped from a height, it accelerates and falls down. Name the force which accelerates the object.

When an object is dropped from a height, it accelerates and falls down. Name the force which accelerates the object.

When an object is dropped from a height, it accelerates and falls down. Name the force which accelerates the object.

Give the formula for the gravitational force F between two bodies of masses M and m kept at a distance d from each other.

Mass of an object is 10 kg. what is its weight on earth ?

The value of acceleration due to gravity of earth :A. is the same on equator and polesB. is the least on polesC. is the least on equatorD. increase from pole to equator

Calculate the gravitational force on a body of mass 1 kg lying on the aurface of earth. Given mass of earth. Given mass of earth is `6xx10^(24)` kg and radius of earth is 6400 km.

The mass of the Earth is `6xx10^(24)kg`. The distance between the Earth and the sun is `1.5xx10^(11)m`. If the gravitational force between the two is `3.5xx10^(22)N` what is the mass of the sun? `G=6.7xx10^(-11) Nm^(2)//kg^(2)`

What is the magnitude of the gravitational force between the Earth and a 1kg object on its surface ? (Mass of the earth is `6xx10^(24)` kg and radius of the Earth is `6.4xx10^(6) m)`.

Write true or false for the following statements:Acceleration due to gravity is expressed asg =G\(\frac{M}{R^2}\)Where, symbols have their usual meanings.

Assessment (A) : The net force which change only the direction of the velocity of a body is called centripetal force. Reason (R) : Centripetal force exists only in uniform circular motion. A) A and R are trueB) A and R are false C) A is true but R is false D) A is false but R is true

Which of the following statement is true ? Statement 1 : Velocity and acceleration of a body in a uniform circular motion are perpendicular to each other. Statement 2 : The direction of the acceleration of a body in uniform circular motion is always towards its centre. A) 1 B) 2 C) 1 and 2 D) None

For a freely falling body, a = ………………. A) – g B) + g2C) + g3D) + g

A body weighs more at the pole than at the equator, Why?

Write an expression for the mass of the earth.

What are the dimension of gravitational constant G?

Write the formula for the gravitational potential energy of mass 'm' at a finite distance 'r' in the gravitational field of mass M.

What is the value of G?

What is the force of attraction between the earth and a body of mass 1 kg?

Suppose the radius of earth is half of its present value (Mass remaining unchanged). The value of g at a height equal to the final radius is `10 x m//s^(2)`. Find the value of x.

What is the unit of intensity of gravitational field?

What is the value of 'g' and 'G' at the centre of the earth?

What is the effect of altitude on the acceleration due to gravity?

As orbital radius r of a satellite is increased, state which of the following quantities will increase and which will decrease ? (i) Orbital speed (ii) Time period (iii) Frequence (iv) Angular speed (v) Kinetic energy (vi) Potential energy (vii) Toyal mechanical energy .

What is meant by weightlessness?

What is the value of gravitational potential energy at infinity?

A geostationary satellite is orbiting the earth at a height of `6R` above the surface oof earth where R is the radius of the earth .The time period of another satellite at a distance of `3.5R` from the centre of the earth is ….. hours.

The force due to gravity upon an object is known as its ………… A) frictional force B) gravitational force C) weight force D) both B &amp; C

The escape velocity v of a body depends on 1. the acceleration due to gravity ‘g’ and 2. the radius of planet ‘R’Find the relation between them using dimension analysis.

Two particles A and B of masses 1 kg and 2 kg respectively are kept 1 m apart and are released to move under mutual attraction. Find The speed A when that of B is 3.6 cm/hr. What is the separation between the particles at this instant?

Class 9 Science MCQ Questions of Gravitation with Answers?

set Aset Bv = u + atas = ut + \(\cfrac{1}2\) at2h = \(\cfrac{gt^2}2\)v2 – u2 = 2asbSet A are the equations of uniform accelerated motion. Set B are the equations of a free fall body. Then a & b areA) v = -gt, v2 = -2gh B) v = gt, v2 = 2.gh C) v = g – t, v2 – g2 = 2h D) A or B

The force due to gravity upon an object is known as its ………… A) frictional force B) gravitational force C) weight force D) both B & C