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Physics

HomePhysicsPage 42

Assertion : Mass and energy are not conserved separately, but are conserved as a single entity called mass-energy. Reason : Mass and energy conservation can be obtained by Einstein equation for energy.

(a)       If both assertion and reason are true and the reason is the correct explanation of the assertion. (b)       If...

37. A person supports a book between his finger and thumb as shown (the point of grip is assumed to be at the corner of the book). If the book has a weight of W then the person is producing a torque on the book of

(a)    w. a/2    anticlockwise (b)     w. b/2  anticlockwise (c)      wa anticlockwise (d)     wa  clockwise...

23. Assertion : Heavy water is used as moderator in nuclear reactor. Reason : Water cool down the fast neutron.

(a)       If both assertion and reason are true and the reason is the correct explanation of the assertion. (b)       If...

Assertion : Graph between potential energy of a spring versus the extension or compression of the spring is a straight line. Reason : Potential energy of a stretched or compressed spring, proportional to square of extension or compression.

(a)       If both assertion and reason are true and the reason is the correct explanation of the assertion. (b)       If...

36. When a force of 6.0 N is exerted at 30 degree to a wrench at a distance of 8 cm from the nut, it is just able to loosen the nut. What force F would be sufficient to loosen it, if it acts perpendicularly to the wrench at 16 cm from the nut

(a)  3 N (b)  6 N (c)   4 N (d)  1.5 N Ans. d

Assertion : Wire through which current flows gets heated. Reason : When current is drawn from a cell, chemical energy is converted into heat energy.

(a)       If both assertion and reason are true and the reason is the correct explanation of the assertion. (b)       If...

A cubical block of side L rests on a rough horizontal surface with coefficient of friction μ . A horizontal force F is applied on the block as shown. If the coefficient of friction is sufficiently high so that the block does not slide before toppling, the minimum force required to topple the block is

(a) Infinitesimal (b)  mg/4 (c)   mg/2 (d)  mg(1-μ) Ans. c

20. Assertion : Work done by or against gravitational force in moving a body from one point to another is independent of the actual path followed between the two points. Reason : Gravitational forces are conservative forces.

(a)       If both assertion and reason are true and the reason is the correct explanation of the assertion. (b)       If...

Assertion : A quick collision between two bodies is more violent than slow collision, even when initial and final velocities are identical. Reason : The rate of change of momentum determine that force is small or large.

a) If both assertion and reason are true and the reason is the correct explanation of the assertion. (b)       If...

33. Two men are carrying a uniform bar of length L , on their shoulders. The bar is held horizontally such that younger man gets (1/4)th load. Suppose the younger man is at the end of the bar, what is the distance of the other man from the end

(a)      L/3 (b)      L/2 (c)      2L/3 (d)     3L/4 Ans. c

What is the torque of the force F vector =(2iˆ-3jˆ+4kˆ)Nacting at the pt. r vector = (3iˆ+2jˆ+ 3kˆ)M about the origin

(a)        -17iˆ+6jˆ+13kˆ (b)     -6iˆ+6jˆ-12kˆ (c)  17iˆ-6jˆ-13kˆ (d) 6iˆ-6jˆ+12kˆ Ans. c

Assertion : A kinetic energy of a body is quadrupled, when its velocity is doubled. Reason : Kinetic energy is proportional to square of velocity

(a)       If both assertion and reason are true and the reason is the correct explanation of the assertion. (b)       If...

Assertion : Power developed in circular motion is always zero. Reason : Work done in case of circular motion is zero.

(a)       If both assertion and reason are true and the reason is the correct explanation of the assertion. (b)       If...

Assertion : A body cannot have energy without having momentum but it can have momentum without having energy. Reason : Momentum and energy have same dimensions.

(a)       If both assertion and reason are true and the reason is the correct explanation of the assertion. (b)       If...

Assertion : In an elastic collision of two bodies, the momentum and energy of each body is conserved. Reason : If two bodies stick to each other, after colliding, the collision is said to be perfectly elastic.

(a)       If both assertion and reason are true and the reason is the correct explanation of the assertion. (b)       If...

Assertion : When the force retards the motion of a body, the work done is zero. Reason : Work done depends on angle between force and displacement.

(a)       If both assertion and reason are true and the reason is the correct explanation of the assertion. (b)       If...

Assertion : According to law of conservation of mechanical energy change in potential energy is equal and opposite to the change in kinetic energy. Reason : Mechanical energy is not a conserved quantity.

(a)       If both assertion and reason are true and the reason is the correct explanation of the assertion. (b)       If...

Assertion : The power of a pump which raises 100 kg of water in 10sec to a height of 100 m is 10 KW. Reason : The practical unit of power is horse power.

(a)       If both assertion and reason are true and the reason is the correct explanation of the assertion. (b)       If...

Assertion : Water at the foot of the water fall is always at different temperature from that at the top. Reason : The potential energy of water at the top is converted into heat energy during falling.

(a)       If both assertion and reason are true and the reason is the correct explanation of the assertion. (b)       If...

Assertion : The rate of change of total momentum of a many particle system is proportional to the sum of the internal forces of the system. Reason : Internal forces can change the kinetic energy but not the momentum of the system.

(a)       If both assertion and reason are true and the reason is the correct explanation of the assertion. (b)       If...

Assertion : The change in kinetic energy of a particle is equal to the work done on it by the net force. Reason : Change in kinetic energy of particle is equal to the work done only in case of a system of one particle.

(a)       If both assertion and reason are true and the reason is the correct explanation of the assertion. (b)       If...

34. A uniform meter scale balances at the 40 cm  mark when weights of 10g and 20g are suspended from the 10 cm and 20cm marks. The weight of the metre scale is

(a)     50g (b)     60g (c)     70g (d)      80g Ans. c

Assertion : The work done during a round trip is always zero. Reason : No force is required to move a body in its round trip.

(a)       If both assertion and reason are true and the reason is the correct explanation of the assertion. (b)       If...

8. A rocket is propelled by a gas which is initially at a temperature of 4000 K. The temperature of the gas falls to 1000 K as it leaves the exhaust nozzle. The gas which will acquire the largest momentum while leaving the nozzle, is

  (a)  Hydrogen                          (b)  Helium (c)   Nitrogen                            (d)  Argon Ans. d

Assertion : Comets move around the sun in elliptical orbits. The gravitational force on the comet due to sun is not normal to the comet’s velocity but the work done by the gravitational force over every complete orbit of the comet is zero. Reason : Gravitational force is a non conservative force.

(a)       If both assertion and reason are true and the reason is the correct explanation of the assertion. (b)       If...

Assertion : A spring has potential energy, both when it is compressed or stretched. Reason : In compressing or stretching, work is done on the spring against the restoring force.

(a)       If both assertion and reason are true and the reason is the correct explanation of the assertion. (b)       If...

18. One day on a spacecraft corresponds to 2 days on the earth. The speed of the spacecraft relative to the earth is

(a) 1.5 x 10 ^ 8 ms ^-1                   (b)  2. 1 x...

Assertion : The instantaneous power of an agent is measured as the dot product of instantaneous velocity and the force acting on it at that instant. Reason : The unit of instantaneous power is watt.

(a)       If both assertion and reason are true and the reason is the correct explanation of the assertion. (b)       If...

17. A stick of 1 m is moving with velocity of 2.7 x 10 ^ 8 ms ^-1 . What is the apparent length of the stick  (c = 3 x 10 ^ 8 ms ^-1)

(a)  10 m                                   (b)  0.22 m (c)   0.44 m                               (d)  2.4 m Ans. c

Assertion : When a gas is allowed to expand, work done by gas is positive. Reason : Force due to gaseous pressure and displacement (of piston) are in the same direction.

(a)       If both assertion and reason are true and the reason is the correct explanation of the assertion. (b)       If...

15. A pulley fixed to the ceilling carries a string with blocks of mass m and 3 m attached to its ends. The masses of string and pulley are negligible. When the system is released, its centre of mass moves with what acceleration

(a)  0                                         (b) g/4 (c)   g/2                             ...

3. Assertion : Work done by friction on a body sliding down an inclined plane is positive. Reason : Work done is greater than zero, if angle between force and displacement is acute or both are in same direction.

(a)       If both assertion and reason are true and the reason is the correct explanation of the assertion. (b)       If...

Assertion : A person working on a horizontal road with a load on his head does no work. Reason : No work is said to be done, if directions of force and displacement of load are perpendicular to each other.

(a)       If both assertion and reason are true and the reason is the correct explanation of the assertion. (b)       If...

11. The vector sum of two forces is perpendicular to their vector differences. In that case, the force

(a)  Are equal to each other in magnitude (b)  Are not equal to each other in magnitude (c)   Cannot be...

10. A false balance has equal arms. An object weigh X when placed in one pan and Y when placed in other pan, then the weight W of the object is equal to

(a)     √X Y (b) X + Y / 2 (c) X2 + Y2 / 2 (d) 2 / √X2 +...

5. Three weights W, 2W and 3W are connected to identical springs suspended from a rigid horizontal rod. The assembly of the rod and the weights fall freely. The positions of the weights from the rod are such that

(a)      3W will be farthest (b)  W will be farthest (c)   All will be at the same distance (d)  2W...

A ship of mass 3 x 10 ^7 kg initially at rest is pulled by a force of 5 x 10 ^ 4 N through a distance of 3 m. Assume that the resistance due to water is negligible, the speed of the ship is

(a)      1.5 m/s                                      (b)  60 m/s (c)   0.1 m/s                              (d)  5 m/s Ans. c

2. A closed compartment containing gas is moving with some acceleration in horizontal direction. Neglect effect of gravity. Then the pressure in the compartment is

(a)  Same everywhere             (b)  Lower in front side (c)   Lower in rear side            (d)  Lower in upper side Ans. b

A body moves from rest with a constant acceleration. Which one of the following graphs represents the variation of its kinetic energy K with the distance travelled x ?

Answer:  c  

The graph between E and v is

Answer:    a

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