40048 + Interview Questions in Physics in Class 11

1.	Only stationary object is in equilibrium.
Answer» ANSWER :False. When resultant of all FORCES acting on a body is ZERO, then only it is in equilibrium.

Discussion

2.	The angular velocity of a particle rotates with constant speed on only one circle about a fixed axis is constant but its linear velocity changes.. It is possible? Why?
Answer» Solution :Yes. The direction of velocity in CIRCULAR path constantly changes and hence LINEAR velocity is not constant. Here AXIS is fixed and circular path is only ONE. Hence the ANGULAR velocity is obtained parallel to the axis and so it is constant.

Discussion

3.	A ball of mass m and radius r is released in a viscous fluid. The value of its terminal velocity is proportional to
Answer» 1/r m/r `sqrtm/r` m only Answer :B

Discussion

4.	Define angular displacement and angular velocity.
Answer» SOLUTION :ANGULAR displacement : The ANGLE described by the particle about the AXIS of ROTATION in a given time is called angular displacement. Angular velocity : The rate of change of angular displacement is called angular velocity .

Discussion

5.	A and B are two vectors in a plane at an angle of 60^(@) with each other. C is another vector perpendicular to the plane containing vector A and B. Which of the following releations is possible?
Answer» `A+B=C` `A+C=B` `AxxB=C` `AxxC=B` ANSWER :C

Discussion

6.	A solid metal ball has a spherical cavity. If the ball is heated, the volume of the cavity will
Answer» INCREASE decrease remain UNAFFECTED remain unaffected but the SLOPE of the CAVITY will change. Solution :increase

Discussion

7.	A block is placed on a horizontal platform. The system is making horizontal oscillations about a fixed point with a frequency of 0.5Hz. Find the maximum amplitude of oscillation if the block is not to slide on the horizontal platform ? (Coefficient of friction between the block and the platform = 0.2) (g =10 ms^(-2))
Answer» `(2)/(pi^(2))` `(5)/(pi^(2))` `(3)/(pi^(2))` `(4)/(pi^(2))` Answer :A

Discussion

8.	Maximum and minimum magnitudes of the resultant of two vectors of magnitudes P and Q are found to be in the ratio 3 : 1. Which of the following relations is true ?
Answer» <P>P = Q P = 2Q P = 4Q P = Q/3 Answer :B

Discussion

9.	A uniform rod of length I and mass m is suspended by two vertical inextensible string as shown in the fig. The tension in the left string when right string snaps, is:
Answer» `(MG)/4` `(3MG)/4` `(mg)/2` `(mg)/8` ANSWER :A

Discussion

10.	A capillary tube is dipped in water with is lower end 10 cm below the surface. Water rises in the tube to a height of 5 c in. The pressure required to blow a bubble at the lower end of the tube will be
Answer» `1 xx 10^(5) "N/m"^(2)` `1.015 xx10^(5) "N/m"^(2)` `2 xx 10^(5) "N/m"^(2)` `2.5 xx 10^(5) "N/m"^(2l)` ANSWER :B

Discussion

11.	Assertion : A solid sphere and a hollow sphere both of same material are immersed in a liquid , then change in weight in both the spheres will be same. Reason : Upthrust depends upon the volume of the solid immersed not the mass.
Answer» If both Assertion and Reason are CORRECT and Reason is the correct explanation of Assertion. If both Assertion and Reason are TRUE but Reason is not the correct explanation of Assertion. If Assertion is true but Reason is false. If Assertion is false but Reason is true. Solution :UPTHRUST= WEIGHT of fluid displaced =volume of body `xx rho_("fluid")xxg`.

Discussion

12.	Three samples of the same gas A,B and C (gamma=3//2) have initially equal volume. Now the volume of each sample is doubled. The process is adiabatic for A. Isobaric for B and isothermal for C. If the final pressures are equal for all three samples, find the ratio of their initial pressures
Answer» `2:1:SQRT(2)` `2sqrt(2):1:2` `sqrt(2):1:2` `sqrt(2):2:1` Solution :Let `P_(A),P_(B),P_(C)`be the INITIAL pressures of the three samples and P be the final PRESSURE of each for A, the process is ADIABATIC `P_(A)(V)^(3//2)=P(2V)^(3//2), P_(A)=P2^(3//2)` For B, the process is isobaric `P_(B)=P` for C, the process is isothermal `P_(C )(V)=P(2V),2P` Hence `P_(A):P_(B):P_(C )=2^(2//3):1:2=2sqrt(2):1:2`

Discussion

13.	A plane mirror is placed at the bottom of a tank containing a liquid of refractive index mu. P is a small object at a height h above the mirror. An observer O, vertically above P, outside the liquid, observe P andits image in the mirror. The apparent distance between these two will be:
Answer» `2MU h` `(2h)/mu` `(2h)/(mu-1)` `h(1+1/mu)` ANSWER :B

Discussion

14.	A mass of 10 kg is suspended by a rope of length 2.8m from a ceiling. A force of 98 N is applied at the midpoint of the rope as shown in figure. The angle which the rope makes with the vertical in equilibrium is
Answer» `30^(@)` `60^(@)` `45^(@)` `90^(@)` Solution :`"ACCORDING to Lami.s theorem"(F_(1))/(SIN ALPHA)=(F_(2))/(sin beta)`

Discussion

15.	Which of the following is a dimensional constant
Answer» REFRACTIVE INDEX dielectric CONSTANT relative DENSITY gravitational constant ANSWER :D

Discussion

16.	The earth receives 8.4J/minute/ m^2energy from the sun. If he solar energy in 10xx10^4 m^2area is concentrated in a cupfilled with 100 g water at 0^@C The time during which water will boil (in sec) is :
Answer» ANSWER :3

Discussion

17.	A flywheel of M.I. 6 xx10 kgm^(2) is rotating with an angular velocity of 20 rads^(-1). The torque required to bring it to rest in 4s is
Answer» `1.6Nm` `0.6Nm` `0.8Nm` `0.3Nm` ANSWER :D

Discussion

18.	An Earth satellite is moving around the Earth in circular orbit. In such case, which of the following is conserved?
Answer» velocity linear momentum angular momentum none of these Answer :C

Discussion

19.	Just as precise measuremnts are necessary in scienceit is equallyimportant to be able to make rough estimates of quantities using rudinmentary ideas and common observations. Think of ways by which you can estimatethe following (where an estimate is difficult to obtain, try to get an upper bound on the quantity): (a) the total mass of rain - bearing clouds over india during the Monsoon, (b) the mass of an elephant, (c ) the wind speed during a strom, (d) the number of strands of hair on your head, (e ) The number of air molecules in your class room.
Answer» Solution :(a) The total mass of rain bearing clouds over india during the monsoon During the monsson,meterologist record about 100 cm of rain fall, i.e., h =100 cm =1m. Area of our conutry, A = 3.3 million square `km = 3.3xx10^6(10^3m)^2 = 3.3xx10^(12)m^2` :. volume of rain water,`V = Axxh = 3.3xx10^(12)xx1m^3` As density of water, `rho = 10^3 km//m^3` :. Mass of rain water `= V rho = 3.3xx10^(12)xx10^3 kg = 3.3xx10^(15)kg.` This must be the total mass of rainbering clouds over india. (b) Mass of and elephent To estimate the mass of an elephant, we take a boat of known base area A. Measure the depthe of boat in water. Let it be `x_1` Therefore, volume of water displaced by the boat, `V_1= A x_1` Move the elephen into this boat. The boat gets DEEPER into water. Meausre the depth of boat now into mater Let it be `x_2` :. Volume of water displaced by boat and elephant `V_2 = A x_2` :. volume of water displaced by the elephant `V = V_2 - V_1 = A(x_2 -x_1)` If `rho` is density of water, then mass of elephent= mass of water displaced by it =`V rho = A(x_2 -x_1)rho.` (c ) The wind speed during a storm can be estimated USING a gas filled ballon. in fig 1 (NCT).1 OA is normal position of a gas filled balloon, when there is no wind. As the wind blows to the RIGHT, the balloon drifts to position B in one second. The angle of drift `/_ AOB = theta` is MEASURED. If h is the height of the balloon, the `AB = d=h theta.,` This is the distance travelled by the balloon in one second. it must be the wind speed. (d) The NUMBEROF strands of hair on our head For this, we measure the area of the head the carries the hair. Let it be. A. Using a screw gauge, we measure thickness of hair. Let it be d. :. area of cross section of hair ` = pi//2` Assuming that the distribution of hair over the head is uniform, the number of starnds of hair ` =("total area")/("area fo cross secion of each hair") = (A)/(pid^2)` Calculation show that number of strands of hair on human head is of the order of one million. (e ) Number of air molecules in class room Measure the volmue fo room. We know that one mole of air at NTP occuopies a volume of 22.4 liters, `i.e. 22.4 xx10^(-3)m^3` :. Number of air molecules in `22.4xx10^(-3)m^36.023 xx10^(23)` Number of air molecules in volume V of room ` = (6.023xx10^(23))/(22.4xx10^(-03)) xxV = 2.96xx10^(25)V`

Discussion

20.	A particle moves on a straight line a uniform velocity. Its angular momentul (pick up the correct statement)
Answer» is ALWAYS zero is zero about a point on the STRAIGHT line is not zero about a point away from the straight line about any GIVEN point REMAINS constant Answer :B::C::D

Discussion

21.	Which of the following bulk modulus is possible in solid, liquid and gaseous ?
Answer» SOLUTION :BULK MODULUS.

Discussion

22.	If a satellite is revolving around a planet of mass m in an elliptical orbit of semi major axis .a. the orbitral speed of the satellite when it is at a distance r from the focus is
Answer» `sqrt(GM[(2)/(R)-(1)/(a)])` `sqrt(Gm[(2)/(r^(2))-(1)/(a)])` `sqrt(Gm[(2)/(r^(3))-(1)/(a)])` `sqrt(Gm[(2)/(r)-(1)/(a)])` Answer :A

Discussion

23.	A sphere of mass m_(1)collides with a sphere of mass m_(2) which is at rest. Prove that whatever be the initial direction of the first sphere, it will move off at right angles to the line of centres at the time of collision if the coefficient of restitution is m_(1)//m_(2).
Answer» ANSWER :N//a

Discussion

24.	A ball of mass 2kg hanging from a spring oscillates with a time period 2p seconds . Ball is removed when it is in equilibrium position , the spring shortens by
Answer» `(G)m` `(g/2)` `(2G)m` `(2P)m` ANSWER :A

Discussion

25.	Give the uses of visosity.
Answer» Solution :(i) High viscosity liquids are used in buffers in trains shunting so that the shocks may be absorbed easily. (ii)Blood viscosity plays most important role in the blood circulation in human arteries. (III)Millikanhad used viscous force in his experiment ofr finding electronic chagre of an ELECTRON . (iv)In vehicle bearing PUMPS all that fun STUFF needs to be lubricated with the correct viscosity fluid.

Discussion

26.	Displacement of SHM particle is x= 5 sin pi t where x is in cm. Then how much time taken by the particle from the mean position to at maximum displacement.
Answer» SOLUTION :`x= 5SIN pi t` Maximum distance x= 5 cm `therefore 5= 5 SIN pi t` `therefore 1= sin pi t` `therefore (pi)/(2) = pi t` `therefore t= (1)/(2)s`.

Discussion

27.	Two non zero vectors vecA "and" vecB are such that \|vecA+vecB\|=\|vecA - vecB\|. Find angle between vecA "and " vecB?
Answer» SOLUTION :`\|vecA+vecB\|=\|vecA-vecB\| RARR A^(2)+B^(2) +2ABcos theta=A^(2)+B^(2)-2AB cos theta` `rArr 4AB cos theta=0 rArr cos theta =0rArr theta=pi/2`

Discussion

28.	Spring A and B are identical except that A is stiffer than B, i.e., Force constant k_(A)gtk_(B). In which spring is more work expended if they are stretched by the same amount ?
Answer» SOLUTION :`W=1/2Kx^(2)` `THEREFORE W_(A)/W_(B)=K_(A)/K_(B), "for some x"` `"as" K_(A)gtK_(B) "so" W_(A)gtW_(B)`

Discussion

29.	Using a screw gauge the diameter of a wire is found to be, 1.51 mm, 1.53mm, 1.48 mm, 1.49 mm, I.51mm, 1.54 mm. The true value of the diameter of the wire is (in mm)
Answer» 1.49 1.52 1.51 0.151 Answer :C

Discussion

30.	An infinite number of particles each of mass 1kg are placed on the positive x-axis at 1m, 2m, 4m, 8m.... from the origin. The magnitude of the resultant gravitational force on 1kg mass kept at the origin is
Answer» 0 G `(3G)/4` `(4G)/3` Answer :D

Discussion

31.	Density remaining constant, if earth contracts to half of its present radius, duration of the day would be in minutes)
Answer» 45 80 100 120 Answer :A

Discussion

32.	The mean translational kinetic energy of a perfect gas molecule at the temperature Tk is :
Answer» `k_BT` `3/2k_BT` `1/2k_BT` `2K_BT` SOLUTION :K.E `= in 3/2 k_BT [:' k = k_B]`

Discussion

33.	Can you explain the translation of a car by the translation of a single particle? Justify your answer.
Answer» SOLUTION :Yes, the translation of a single particle can describe that of a car. A car is a combination of a LARGE NUMBER of particles. By the DEFINITION of translation each of these particles has a motion identical to that of the OTHERS. So the motion of any one of the particles is sufficient to describe the motion of the car.

Discussion

34.	A constance force of 200 N displaces a body through 5 m in the direction of the force. Find the work done on the body.
Answer» Solution :`W = VECF .vecs = Fs = 200 xx 5 = 1000 J`

Discussion

35.	A body is projected vertically up with velocity u from a tower. It reaches the ground with velocity nu. The height of the tower is H=u^(2)/(2g) (n^(2)-1).
Answer» Solution :`V^(2)-U^(2)=2as, "Here u=u, v=NU, a=-g, s=-H"` `(nu)^(2)-u^(2)=2gH ` `(n^(2)-1)u^(2)=2gH ""H=(u^(2))/(2g) (n^(2)-1)`

Discussion

36.	A block of mass .M. moving on the firctionless , horizontal surface collides with the spring of spring constant .k.. The other end of the spring is rigidly fixed to a vertical wall. If the spring is compressed by L, the maximum momentum of the block after collision is :
Answer» `SQRT(Mk)L` `(KL^(2))/(2M)` Zero `(ML^(2))/K` Answer :A

Discussion

37.	A stone is lying in a fluid stream. The force acting on it depends on the density of the fluid, the velocity of flow and the maximum area of cross-section perpendicular to the direction of flow. The force F and the velocity v of flow are related as
Answer» `F prop (1)/(V)` `F prop v` `F prop v^(2)` `F prop (1)/(v^(2))` Solution :LET `F= kd^(a)v^(b)A^(c)` Where K is a dimensional constant `:. [MLT^(-2)]= [ML^(-3)]^(a)[LT^(-2)]^(b)[L^(2)]^(c)= [M^(a)L^(-3a+b+2c)T^(-b)]` Applying the principle of HOMOGENEITY of dimensions, we get a=1 and -b= -2 or b=2 `:. F prop v^(2)`

Discussion

38.	Two balls at the same temperature collide. What is conserved?
Answer» MOMENTUM KE Temperature Velocity Answer :A

Discussion

39.	the earth stops rotating
Answer» Solution :If the EARTH STOPS ROTATING,`omega=0 and g^.=g`. Thus the effective value of g INCREASES by `omega^2R cos^2theta`.

Discussion

40.	The velocity of water current in a river changes with distance along the perpendicular to the river according to the law u=(2u_(0))/(d)y " for " 0 le yle (d)/(2) where u_(0)= velocity in the mid-stream d= width of the river =(2 u_(0))/(d)(d-y) " for " (d)/(2) le y le d. A boat travels from a point O on one block of the river to the opposite bank and its steering angle is constantly changedto keep its relative velocity perpendicular to the river current. Calculate the time in which the boat will reach the other bank. The velocity of the boat in still water is u_(0).
Answer» ANSWER :`(PI d)/(2 u_(0))`

Discussion

41.	If (vec(A) + vec(B)) is perpendicular to vec(B) and (vec(A) + 2 vec(B)) is perpendicular to vec(A), then
Answer» `A = sqrt2B` A = 2B 2A = B A = B Answer :A

Discussion

42.	Given below are densities of some solids and liquids. Give rough estimates of the size of their atoms : [Hint : Assume the atoms to be ‘tightly packed’ in a solid or liquid phase, and use the known value of Avogadro’s number. You should, however, not take the actual numbers you obtain for various atomic sizes too literally. Because of the crudeness of the tight packing approximation, the results only indicate that atomic sizes are in the range of a few Å ].
Answer» Solution :ATOMIC mass of a substance = M Density of the substance = `rho` AVOGADRO’s number = `N = 6.023 × 10^23` VOLUME of each atom `=4/3pir^3` Volume of N number of molecules `=4/3pir^3` N … (i) Volume of one mole of a substance `= (M)/(rho)` `=4/3pir^3 N=(M)/(P)` ` therefore r=root3((3M)/(4pirhoN)` For carbon: `M = 12.01 × 10^(–3) KG,` `rho = 2.22 × 10^3 kg m^(–3)` `thereforer=((3xx12.01xx10^-3)/(4pixx2.22xx10^3xx6.023xx10^23))^(1/3)` = 1.29 Å Hence, the radius of a carbon atom is 1.29 Å. For gold: ` M=197.00XX10^(-3) kg` `rho=19.32xx10^(3) kg m^(-3)` `thereforer=((3xx197xx10^-3)/(4pixx19.32xx10^3xx6.023xx10^23))^(1/3)` =1.59 Å Hence ,the radius of a gold atom is 1.59 Å For liquid nitrogen: `M=14.01xx10^(-3) kg ` `rho=1.00xx10^3 kg m^(-3)` `thereforer=((3xx14.01xx10^-3)/(4pixx1.00xx10^3xx6.023xx10^23))^(1/3)` =1.77 Å Hence, the radius of a liquid nitrogen atom is 1.77 Å. For lithium: `M=6.94 xx 10^(-3) kg ` `rho = 0.53xx10^3 kg m^(-3)` `thereforer=((3xx6.94xx10^-3)/(4pixx0.53xx10^3xx6.023xx10^23))^(1/3)` For liquid flurorine`M = 19.00 xx 10^(–3)` kg `rho = 1.14 × 103 kg m^(–3)` `thereforer=((3xx19xx10^-3)/(4pixx1.14xx10^3xx6.023xx10^23))^(1/3)` = 1.88 ÅHence, the radius of a liquid FLUORINE atom is 1.88 Å

Discussion

43.	Assertion- Vector product of two vectors may be greater then , equal to or less than the scaler product . Reason At theta=45^(@) two are equal .
Answer» If both Assetion and Reason are correct but Reason is the correct explanation of Assertion. If both Assetion and Reason are correct but Reason is not the correct explanation of Assertion. If Asserion is true but Reason is FALSE If Asserion is false but Reason is true Solution :(B) `\|AxxB\|=AB SIN thetaand A.B =AB costheta`

Discussion

44.	A barometer contains two uniform capillaries of radii 1.44 xx 10^(-3) m and 7.2 xx 10^(-4) If the height of liquid in narrow tube is 0.2m more than that in wide tube, the true pressure difference is computed to be P xx 310 N//m^2 Density of liquid = 10^3 kg//m^3, surface tension = 72 xx 10^(-3)N/m and g= 9.8m//s^2 Find P.
Answer» ANSWER :6

Discussion

45.	The error in the measurement of radius of a sphere is 0.4%. The percentage error in its volume is
Answer» 0.0016 0.0012 0.0024 0.012 Answer :D

Discussion

46.	The velocity of sound in any gas depends upon
Answer» WAVELENGTH of sound only density and ELASTICITY of gas intensity of sound WAVES only. Amplitude and frequency of sound ANSWER :B

Discussion

47.	What is the effect of pressure on the fusion and boiling point of water?
Answer» SOLUTION :The BOILING point INCREASES and the MELTING point decreases with pressure.

Discussion

48.	A force of 5N is applied on a 20 Kg mass at rest. The work doen in the third secondis
Answer» `25/8J` `25/4J` `12J` `25J` ANSWER :A

Discussion

49.	Choose the correct alternative. Gravitational force/Weak miclear force is the weakest fundamental force.
Answer» SOLUTION :GRAVITATIONAL FORCE

Discussion

50.	A cylinder of mass m is suspended through two strings wrapped around it as shwon in figure . Find (a). the tension T in the string and (b). the speed o the cylinder as it falls through a distance h.
Answer» Solution :There is no horizontal force acting on the cylinder. The centre of MASS of the cylinder falls vertically downwards, The cylinder rolls down without slipping. Let the acceleration of the centre of mass of the cylinder be a. Then the ANGULAR acceleration is a `a=a/r` For the motion of the centre of mass `mg -2T =ma`.........(i) The torque acting on the cylinder is `tau = lalpha` `Tr + Tr -(1/2 mr^(2)) xx a/r` `2Tr =1/2mar, T = 1/4 ma` SUBSTITUTING in EQNS (i) `mg -1/2 ma = ma` `3/2 ma = mg, a=(2g)/3 = (2 xx 9.8)/3 = 6.53 m//s^(2)` `T = 1/4 ma = 1/4 xx (2 xx 2 xx 9.8)/3` Tension in the cords are 3.27 N each = 3.27 N

Discussion

Explore topic-wise InterviewSolutions in Current Affairs.

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A ball of mass 2kg hanging from a spring oscillates with a time period 2p seconds . Ball is removed when it is in equilibrium position , the spring shortens by

Give the uses of visosity.

Displacement of SHM particle is x= 5 sin pi t where x is in cm. Then how much time taken by the particle from the mean position to at maximum displacement.

Two non zero vectors vecA "and" vecB are such that |vecA+vecB|=|vecA - vecB|. Find angle between vecA "and " vecB?

Spring A and B are identical except that A is stiffer than B, i.e., Force constant k_(A)gtk_(B). In which spring is more work expended if they are stretched by the same amount ?

Using a screw gauge the diameter of a wire is found to be, 1.51 mm, 1.53mm, 1.48 mm, 1.49 mm, I.51mm, 1.54 mm. The true value of the diameter of the wire is (in mm)

An infinite number of particles each of mass 1kg are placed on the positive x-axis at 1m, 2m, 4m, 8m.... from the origin. The magnitude of the resultant gravitational force on 1kg mass kept at the origin is

Density remaining constant, if earth contracts to half of its present radius, duration of the day would be in minutes)

The mean translational kinetic energy of a perfect gas molecule at the temperature Tk is :

Can you explain the translation of a car by the translation of a single particle? Justify your answer.

A constance force of 200 N displaces a body through 5 m in the direction of the force. Find the work done on the body.

A body is projected vertically up with velocity u from a tower. It reaches the ground with velocity nu. The height of the tower is H=u^(2)/(2g) (n^(2)-1).

A block of mass .M. moving on the firctionless , horizontal surface collides with the spring of spring constant .k.. The other end of the spring is rigidly fixed to a vertical wall. If the spring is compressed by L, the maximum momentum of the block after collision is :

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What is the effect of pressure on the fusion and boiling point of water?

A force of 5N is applied on a 20 Kg mass at rest. The work doen in the third secondis

Choose the correct alternative. Gravitational force/Weak miclear force is the weakest fundamental force.

A cylinder of mass m is suspended through two strings wrapped around it as shwon in figure . Find (a). the tension T in the string and (b). the speed o the cylinder as it falls through a distance h.