Explore topic-wise InterviewSolutions in .

This section includes InterviewSolutions, each offering curated multiple-choice questions to sharpen your knowledge and support exam preparation. Choose a topic below to get started.

51.

Explain why, buildings and dams have wide foundations.

Answer»

The foundations of buildings and dams are laid on a large area of ground so that the weight of the building or dam produces less pressure on the ground and they may not sink into the ground.
Discussion
52.

Complete the analogy :Shape of the Earth at equator: Bulged :: shape of the Earth at poles:________________

Answer» Flattened- The shape of the Earth is not exactly spherical. Due to its rotation, the earth bulges at the equator andis flattened at the prices.
Discussion
53.

The ratio of the time period of a simple pendulum of length `l_(0)` with a pendulum of infinite length is : (Where, R is the radius of earth)A. zeroB. `sqrt((l_(0))/(R))`C. `sqrt((l_(0) + R)/(R)`D. `sqrt((R)/(I_(0) + R))`

Answer» Correct Answer - B
Discussion
54.

Earth is flattened at poles and bulged at equator. This is due to Tidal waves in the sea are primarily due toA. revolution of earth around the sun in an elliptical orbitB. angular velocity of spinning motion about its axis is more at equatorC. centrifugal force is more at equator than polesD. more centrifugal force at poles than equator

Answer» Correct Answer - C
Discussion
55.

Identify the correct defination of gravitationa potential at a point.A. It is defined in term fo the force required to displaced a unit mass from infinity to that pointB. It is defined in term of the force required to move a unit mass from the surface of earth to that pointC. It is defined in terms of the force required to displace a unit mass from that point to infinityD. none of these

Answer» Correct Answer - D
Discussion
56.

Tidal waves in the sea are primarily due toA. The gravitational effect of the moon on the earthB. The gravitational effect of the sun on the earthC. The gravitational effect of Venus on the earthD. The atmophere effect of the earth itself

Answer» Correct Answer - A
Discussion
57.

Two spherical planets P and Q have the same uniform density `rho,` masses `M_p and M_Q` and surface areas A and 4A respectively. A spherical planet R also has uniform density `rho` and its mass is `(M_P + M_Q).` The escape velocities from the plantes P,Q and R are `V_P V_Q and V_R` respectively. ThenA. `V_(Q)gtV_(R)gtV_(P)`B. `V_(R)gtV_(Q)gtV_(P)`C. `V_(R)//V_(P)=3`D. `V_(P)//V_(Q)=1/2`

Answer» Correct Answer - B::D
`V_(P)=sqrt((2GM)/(R)),V_(Q)=sqrt((2G(8M))/(2R))=2V_(P)`
`V_(R)=sqrt((2G(9M))/(9^(1//3)R))=9^(1//3)V_(P)`
Discussion
58.

Two spherical planets P and Q have the same uniform density `rho,` masses `M_p and M_Q` and surface areas A and 4A respectively. A spherical planet R also has uniform density `rho` and its mass is `(M_P + M_Q).` The escape velocities from the plantes P,Q and R are `V_P V_Q and V_R` respectively. ThenA. `V_Q gt V_R gt V_P`B. `V_R gt V_Q gt V_P`C. `V_P/V_P =3`D. `V_P/ V_ Q =(1)/(2)`

Answer» Correct Answer - B::D
(b,d) Let the mass of P be m.
Then `m = rho xx(4)/(3) pir^3 = rhoxx(4)/(3)pi[(A)/(4pi)]^(3//2)`
The mass of `Q = rho xx(4)/(3) pi[(4A)/(4pi)]^(3//2) = 8m`
`:. The mass of R = 9m`
if the radius of P = r
Then the radius of Q =2r
`[:. r_Q = ((4A)/(4pi))^(3//2) = 2((A)/(4pi))^(3//2)]`
and radius of `R = 9^(1//3)_r`
`[:.( M_R = M_p + M_Q),(r_R^3 =r^3 + (2r)^3 = 9r^3)]`
`Now, v_p = sqrt((2GM_p)/(R_p)) = sqrt((2Gm)/(r )`
`v_Q = sqrt(((2G(9m))/(R_Q)) = sqrt((2G(8m))/(2r)) = 2v_p`
`v_R = sqrt((2G(9m))/(9^1/3_r)) = 9^1//3_(vp)`
Discussion
59.

Explain the term free fall and state the corresponding kinematical equations of motion in the usual notation.

Answer»

When a body falls in air, there are three forces acting on the body : (1) the gravitational force due to the earth, acting downward (2) the force of buoyancy (upthrust) due to air, acting upward I (3) the force due to friction with air (called air resistance), acting upward (being always in the direction opposite to that of the velocity of the body).

Under certain conditions, the force of buoyancy due to air and friction with air can be ignored compared to the gravitational force of the earth. In that case (near the earth’s surface) the body falls with almost uniform acceleration (g). Whenever a body moves under the influence of the force of gravity alone, it is said to be falling freely. Strictly speaking, this is true only if the body falls in vacuum.

The kinematical equations of motion, in the usual i notation, are

v = u + gt, s = ut + \(\frac{1}{2}\) gt2 and v2 = u2 + 2gs.

If the initial velocity (u) of the body is zero, v = gt, s = \(\frac{1}{2}\)gt2 and v2 = 2 gs.
Discussion
60.

If the masses of two bodies are quadrupled and the distance between their centres is doubled, then how many times the force of gravitation between them will be changed ?

Answer» `F_(1)=(Gm_(1)m_(2))/(r^(2))`
`F_(2)=(Gm_(1)m_(2))/(R^(2))`
Here, `M_(1)=4m_(1),M_(2)=4m_(2)` and R = 2r
`therefore F_(2)=(G(4m_(1))(4m_(2)))/((2r)^(2))`
`=(16Gm_(1)m_(2))/(4r^(2))`
`therefore F_(2)=4F_(1)`
Hence, the gravitational force will increase to four times the initial magnitude.
Discussion
61.

(a) How does a boat float in water ? A piece of steel has a volume of `12 cm^(3)`, and a mass of 96 g. What is its density : (i) `in g //cm^(2)` (ii) `in kg//m^(3)`

Answer» Correct Answer - (b) `(I ) 8 g //cm^(3)` (ii ) ` 8000 kg // m^(3)`
Discussion
62.

(a) Define pressure . ( b) What is the relation between pressure force and area ? ( c) Calculate the pressure when a force of 200 N is exerted on an are of : `10m^(2)` `5m^(2)`

Answer» Correct Answer - ( c) (I ) 20 Pa
Discussion
63.

If R is the radius of the earth, the height at which g will decrease by `0.1%` of its value at the surface of the earth isA. R/6400B. R/2000C. R/1000D. R/500

Answer» Correct Answer - b
`g_(h)=g(1-(2h)/(R))=100(1-(2h)/(R))`
`(2h)/(R)=1-(999)/(1000)=(1)/(1000)`
`h=(R)/(2000).`
Discussion
64.

If the mass of one particle is increased by `50 %` and the mass of another particle llis decreased by `50%`, the force between themA. decreases by `25%`B. decreases by `75%`C. increases by `25%`D. does not change

Answer» Correct Answer - A
`F_(1)=G(m_(1)m_(2))/(d^(2))` and `F_(2)=G((m_(1)+(m_(1))/2)(m_(2)-(m_(2))/2))/(d^(2))`
Discussion
65.

If there particles, each of mass `M`, are placed at the three corners of an equilibrium triangle of side, a the force exerted by this system on another particle of mass `M` placed (i) at the midpoint of side and (ii) at the centre of the triangle are, respectively.A. `0,(4GM^(2))/(3a^(2))`B. `(4GM^(2))/(3a^(2)),0`C. `(3GM^(2))/(a^(2)),(GM^(2))/(a^(2))`D. `0,0`

Answer» Correct Answer - B
Find individual forces and calculate resultant Use `F=(Gm_(1)m_(2))/(R^(2))`
Discussion
66.

If there particles, each of mass `M`, are placed at the three corners of an equilateral triangle of side, a the force exerted by this system on another particle of mass `M` placed (i) at the midpoint of side and (ii) at the centre of the triangle are, respectively.

Answer» Correct Answer - A::B::C::D
Discussion
67.

A solid sphere of uniform density and radius 4 units is located with its centre at the origin O of coordinates. Two sphere of equal radii 1 unit, with their centres at A(-2,0 ,0) and B(2,0,0) respectively, are taken out of the solid leaving behind spherical cavities as shown if fig Then: A. `(31GM)/1024`B. `(Gm)/1024`C. `31GM`D. zero

Answer» Correct Answer - D
Let `rho=` density of sphere `R=`radius of sphere, `r=`radius of the spherical cavities.
Mass of the complete sphere `=4/3piR^(3)rho=M`
Mass of the removed sphere `=4/3pir^(3)rho=m`
Here `m=(Mr^(3))/(R^(3))=(M(1)^(3))/((4)^(3))=M/64`
Now `vecI_(r)=vecI+vecI_(P)+vecI_(Q)`
Here `I=0, also vecI_(P)=-vecI_(Q)impliesI_(R)=0`
Discussion
68.

Average density of the earthA. is a complex function of gB. does not depend on gC. is inversely proportional to gD. is directly proportional to g

Answer» Correct Answer - D
(d) `g = (GM)/(R^2) =(GrhoxxV)/(R^2) rArr g = (Gxxrhoxx(4)/(3)piR^3)/(R^2)`
`g = (4)/(3) rhopiG.R whre rho rarr average density`
Discussion
69.

A mass is suspended from a spring having spring constant k is displaced veritcally and relased. It oscillates with period T the weight of the mass suspended is (g= gravitatioanal acceleration)A. `(KTg)/(4pi^(2))`B. `(KT^(2)g)/(4pi^(2))`C. `(KTg)/(2pi^(2))`D. `(KT^(2)g)/(2pi^(2))`

Answer» Correct Answer - b
`T=2pisqrt((m)/(k))`
`T^(2)=4pi^(2)(m)/(k)`
`mg=(kT^(2))/(4pi^(2))g`
`W=(KT^(2))/(4pi^(2))`
Discussion
70.

What is the minimum energy required to launch a satellite of mass m from the surface of a planet of mass M and radius R in a circular orbit at an altitude of 2R?A. `5/3mgR`B. `4/3mgR`C. `5/6mgR`D. `5/4mgR`

Answer» Correct Answer - C
Total energy `E=1/2mv^(2)-(GmM)/r`
`=(GmM)/(2r)-(GMm)/r=-G(mM)/(2r)`
`r=2R=R=3R`
`E=(GmM)/(6R)`
Potential energy `=-(GMm)/R`
Minimum energy required `=1/6(GMm)/R-((-GMm)/R)=5/6(GMm)/R`
Discussion
71.

The gravitational force between two particles separated by a distance r varies as ……..(a) 1/r(b) r(c) r2(d) \(\frac1{r^2}\)

Answer»

Answer is (d) \(\frac{1}{r^2}\)
Discussion
72.

What are polar satellite? Describe their usefulness.

Answer»

Polar satellites are low altitude (h = 500 to 800 km) satellites and go around the poles of the earth in a north-south direction whereas the earth rotates around its axis in east-west direction. The time period of a polar satellite is approximately 100 minutes, hence it crosses any altitude many times a day.

However, since its height is only 500-800 km, a camera fixed on it can view only small strips of the earth in one orbit. Adjacent strips are viewed in the next orbit, so that in effect, the whole earth can be viewed strip by strip during the entire day. These satellite can view polar and equatorial regions at close distances with good resolution. Information gathered from such satellites is extremely useful in remote sensing meterology as well as for environmental studies of the earth.
Discussion
73.

The time period of a satellite of the earth is 10 hours. If the separations between the earth and the satellite is increased to 4 times the previous value, then what will be the new time period of the satellite ?A. 2 hoursB. 10 hoursC. 40 hoursD. 80 hours

Answer» Correct Answer - D
Discussion
74.

Which physical quantity is conserved when a planet revolves around the sun ?A. the angular momentum remins conservedB. the angular speed remains constantC. the linear velocity remains constantD. the linear momentum remains constant

Answer» Correct Answer - A
In the case of planetary motion, no external torque acts on the system. So, angular momentum is conserved.
Discussion
75.

A planet is revolving around the sun as shown in elliptical path. The correct option is A. The time taken in travelling DAB is less than that for BCDB. The time taken in travelling DAB is greater than that for BCDC. The time taken in travelling CDA is less than that for ABCD. The time taken in travelling CDA is greater than that for ABC

Answer» Correct Answer - A
Discussion
76.

A planet is revolving around the sun as shown in elliptical path. The correct option is A. The time taken in travelling DAB is less than that for BCDB. The time taken in travelling DAB is greater than that for BCDC. The time taken in travelling CDA is less than that for ABCD. The time taken in travelling CDA is greater than that for ABC

Answer» Correct Answer - A
During path DAB planet is nearer to sun as comparision with path BCD. So time taken in travelling DAB is less than that for BCD because velocity of planet will be more in region DAB.
Discussion
77.

Supose a planet is revolving around the sun in an elliptical path given by `(x^(2))/(a^(2)) + (y^(2))/(b^(2))=1` Find time period of revolution Angular momentum of the planet about the sun is `L` .

Answer» Rate of area swept `(dA)/(dt) = (L)/(2m)` =constant
`rArr dA = L/(2m)dt`
`underset(A=0)overset(A=piab)intdA=underset(t=0)overset(t=T)int(L)/(2m)dt`
`rArrpiab=(L)/(2m)TrArrT=(2pimab)/(L)` .
Discussion
78.

What is geocentric theory?

Answer»

Ptolemy thought that sun as well as other stars revolved around earth. His theory was called geocentric theory. He said that the planets revolved in small circles known as epicycles whereas centers of these epicycle revolved around the earth in larger circles called deferents.
Discussion
79.

The orbital angular momentum of a satellite revolving at a distance r from the centre is L . If the distance is increased to 16 r, then the new angular momentum will beA. `16 L`B. `64 L`C. `(L)/(4)`D. `4 L`

Answer» Correct Answer - D
`L=mvr=msqrt((GM)/(r))r=m sqrt(GMr)`
`:. L prop sqrt(r)`
`rArr (t_(1))/(t_(2))=sqrt((r_(2))/r_(2))rArr (L)/(L_(2))=sqrt((r_(1))/(r_(2)))" "{(because L_(1)= "L,"),(" "r_(1)=r),(" "r_(2)=16 r):}}`
`rArr (L)/(L_(2))=sqrt((r)/(16r))rArr(L)/(L_(2))=(1)/(4)rArrL_(2)=4L`.
Discussion
80.

If a paper and a book are dropped from same height at a time, they will reach the ground at same time A) if their masses are equal B) if there were no air resistance C) if there is no gravitation D) not possible

Answer»

B) if there were no air resistance
Discussion
81.

Weight of a body on the surface of the earth is W. Then weight of the same body on the surface of a planet whose mass is double that of the earth and radius thrice that of the earth isA) \(\cfrac{9\,W}2\)B) 18 W C) \(\cfrac{2\,W}3\)D) \(\cfrac{2\,W}9\)

Answer»

 D) \(\cfrac{2\,W}9\)
Discussion
82.

Geocentric model was given byA. Claudius PtolemyB. Henry CavendishC. Nicoals CopernicusD. Aryabhatta

Answer» Correct Answer - A
Discussion
83.

The angular momentum `(L)` of the earth revolving round the sun uis proportional to `r^(n)`, where `r` is the orbital radius of the earth. The value of `n` is (assume the orbit to be circular)A. 0.5B. 1C. 1.5D. `2.0`

Answer» Correct Answer - a
`v=sqrt((GM)/(R))`
Angular momentum
`L=mRv=mR sqrt((GM)/(R))=msqrt(GM)R^(1//2)`
`therefore" " L prop R^(1//2)`.
Discussion
84.

The gravitational force of attraction between two bodies is F1 . If the mass of each body is doubled and the distance between them is halved then the gravitational force between them is F2 . Then A) F1 = F2 B) F2 = 4F1C) F2 = 8F1 D) F2 = 16F1

Answer»

D) F2 = 16F1
Discussion
85.

Two celestial bodies are separated by some distance. If the mass of any one of the bodies is doubled while the mass of other is halved then how far should they be taken so that the gravitational force between them becomes one-fourth ?

Answer» Correct Answer - They should be taken to double its distance.
Discussion
86.

What force is responsible for the earth revolving round the sun?

Answer»

Gravitational force is responsible for the earth revolving around the sun.
Discussion
87.

What force is responsible for the earth revolving round the sun ?

Answer» Gravitational force is responsible for the earth revolving round the sun.
Discussion
88.

What force is responsible for the carth revolving round the sun?

Answer» Correct Answer - Gravitational force
Discussion
89.

The gravitational force of attraction between two bodies is `F_(1).` If the mass of each body is doubled and the distance between them is halved, then the gravitational force between them isA. `F_(1)`B. `4F_(1)`C. `8F_(1)`D. `16F_(1)`

Answer» Correct Answer - d
`F_(1)=(Gm_(1)m_(2))/(r_(1)^(2))` and
`F_(2)=(G(2m_(1))(2m_(2)))/((r//2)^(2))`
`(F_(2))/(F_(1))=16`
Discussion
90.

Which force is responsible for the moon revolving round the earth ?

Answer» Gravitational force is responsible for the moon revolving round the earth.
Discussion
91.

Who gave three laws of planetary motion ?

Answer» Answer - kepler.
Discussion
92.

The distance between two objects is doubled. What happens to gravitational force between them ?

Answer» The gravitational force becomes `(1//4)th`.
Discussion
93.

What happens to the gravitational force between two objects when the distance between them is: (i) doubled? (ii) halved?

Answer» Correct Answer - (i) becomes one fourth (ii) becomes four times
Discussion
94.

Name the scientist who gave the three laws of planetary motion.

Answer» Johannes Kepler gave the three laws of planetary motion.
Discussion
95.

What happens to the gravitational force between two objects when the distance between them is : (i) doubled ? (ii) halved ?

Answer»

(i)If we double the distance between two bodies, the gravitational force becomes one-fourth.

(ii)If we halve the distance between two bodies, then the gravitational force becomes four times.
Discussion
96.

Does the acceleration produced in a freely falling body depend on the mass of the body ?

Answer»

No, the acceleration produced in a freely falling body is independent of the mass of the body.
Discussion
97.

Can we apply Newton’s third law to the gravitational force ? Explain your answer.

Answer»

Yes, Newton’s third law of motion holds good for the force of gravitation. This means that when earth exerts a force of attraction on an object, then the object also exerts an equal force on the earth, in the opposite direction.
Discussion
98.

What is the acceleration produced in a freely falling body of mass 10kg?

Answer»

The acceleration produced in a freely falling body of mass 10kg is 9.8 m/s2.
Discussion
99.

Can we apply Newton’s third law to the gravitational force? Explain your answer.

Answer»

Yes, we can apply Newton’s third law to the gravitational force as the earth exerts a force of attraction on an objects such that the force exerted by other objects on the earth is equal and in opposite direction.
Discussion
100.

Fill in the blanks with suitable words: a) The acceleration due to gravity on the moon is about ………. of that on the earth. b) In order that the force of gravitation between two bodies may become noticeable and cause motion, one of the bodies must have an extremely large …………. c) The weight of an object on the earth is about ………… of its weight on the moon. d) The weight of an object on the moon is about ……….. of its weight on the earth. e) The value of g on the earth is about ……….. of that on the moon. f) If the weight of a body is 6N on the moon, it will be about ………… on the earth.

Answer»

a) One-sixth 

b) Mass 

c) Six times 

d) One-sixth 

e) Six times 

f) 36N
Discussion