Tiêu đề 6. Work, Energy & Power.pdf ✅

1. The work done by a force in displacing a particle from x = 4 m to x = –2 m is :- (1) 360 J (2) 240 J (3) –240 J (4) –360J 2. Power supplied to a particle of mass 2 kg varies with time as P = 2 3 2 t watt. Here, t is in seconds. If velocity of particle at t = 0 is v = 0, the velocity of particle at time t = 2s will be : (1) 1 m/s (2) 4 m/s (3) 2 m/s (4) 2 2 / m s 3. A ping-pong ball of mass m is floating in air by a jet of water emerging out of a nozzle. If the water strikes the ping-pong ball with a speed v and just after collision waterfalls dead, the rate of flow (in kg/s) of water in the nozzle is equal to :- 4. Work done by t he conservative forces on a system is equal to– (1) The change in kinetic energy of the system (2) The change in potential energy of the system (3) The change in total mechanical energy of the system (4) None of t he above 5 . The total work done on a particle is equal to the change in its kinetic energy. This is applicable– (1) Always (2) Only if the conservative forces are acting on it (3) Only in inertial frames (4) Only when pseudo forces are absent 6 . A car of mass 500 kg is driven with acceleration 1 m/s2 along straight level road against constant external resistance of 1000 N. When the velocity is 5 m/s the rate at which t he engine is working is– (1) 5 kW (2) 7. 5 kW (3) 2. 5 kW (4) 10 kW 7. The variation of velocity of particle with time moving along a straight line is illustrated in the following figure. The distance travelled by the particle in four seconds is :- (1) 60 m (2) 55 m (3) 25 m (4) 80 m 8. A mass of 5 kg is suspended by a rope of length2m from a ceiling. A force of 50N in the horizontal direction is applied at the mid-point of the rope. The angle made by the rope with the vertical, in equilibrium is :- (1)50° (2)60° (3)30° (4)45° 9. A force acts on a 3 gm particle in such a way that the position of the particle as a function of time is given by x = 3t – 4t2 + t 3 , where x is in meters and t is in seconds. The work done during the first 4 second is:- (1) 384 mJ (2) 168 mJ (3) 528 mJ (4) 541 mJ 10. If velocity of particle moving along x-axis is given as v= k x . Then (a is acceleration) : 11. Figure shows the vertical section of frictionless surface. A block of mass 2 kg is released from the position A; its KE as it reaches the position C is: (1) 180 J (2) 140 J (3) 40 J (4) 280 J 12. A neutron moving with velocity u collides elastically with an atom of mass number A. If the collision is head-on and the initial kinetic energy of neutron is E, then the final kinetic energy of the neutron after collision is : Work, Energy & Power
13. For the given fig. find the speed of block A when  = 60° :- (1) 2 3 m/s (2) 4 m/s (3) 2 m/s (4) None 14. A wire fixed at the upper end stretches by length by applying a force F. The work done in stretching is :- 15. A mass of 2.9 kg is suspended from a string of length 50 cm and is at rest. Another body of mass100 gm which is moving horizontally with a velocity of 150 m/sec strikes it. After striking the two bodies combine together. The tension in the string, when it makes an angle of 60o with the vertical, is :- (1) 135.3 N (2) 165.5 N (3) 142.4 N (4) 90 N A. If both Assertion & Reason are True & the Reason is a correct explanation of the Assertion. B. If both Assertion & Reason are True but Reason is not a correct explanation of the Assertion. C. If Assertion is True but the Reason is False. D. If both Assertion & Reason are False. 16. Assertion :-Surface between the blocks A and B is rough, work done by friction on block B is always negative. Reason :-Total work done by friction on both the blocks is always zero. (1) A (2) B (3) C (4) D 17. Assertion :- Power developed in circular motion is always zero. Reason :- Work done is case of circular motion is zero. (1) A (2) B (3) C (4) D 18. A uniform chain of length 2 m is kept on a table such that a length of 60 cm hangs freely from the edge of the table. The total mass of the chain is4 kg. What is the work done in pulling the entire chain on the table (1) 7.2 J (2) 3.6 J (3) 120 J (4) 1200 J 19. A bullet is fired from a gun. If the gun recoils freely, the kinetic energy of the gun will be (1) Less than that of bullet (2) Equal to that of bullet (3) Greater than that of bullet (4) Zero 20. A heavy body moving with a velocity of 6 ms-1 collides elastically with a light body(whose mass is half of mass of heavy body) at rest. The velocity of light body will be (in ms–1 ) (1) 6 (2) 8 (3) 12 (4) Very large 21. The potential energy of a body of mass m is: U = ax + by Where x and y are position co-ordinates of the particle. The acceleration of the particle is 22. A body covers a distance of 2 m under the influence of a force F = 15 – 4x newton, where x is the distance covered by the particle in metre. The work done by the force is (1) 7 J (2) 11 J (3) 14 J (4) 22 J 23. A particle of mass m is moving in a circular path of constant radius r such that its centripetal acceleration ac is varying
with time t as ac = k2 rt2 . The power delivered to particle is :- 24. Power applied to a particle varies with time as P = (3t2 – 2t + 1) watt, where t is in second. Find the change in its kinetic energy between t = 2s to t = 4s. (1) 32 J (2) 46 J (3) 61 J (4) 102 J 25. A block 'A' of mass M moving with speed u collides elastically with block B of mass m which is connected to block C of mass m with a spring. When the compression in spring is maximum the velocity of block C with respect to block A is (neglect friction) :- 26. A body of mass 2 kg is in influence a force which causes displacement in it given x=t2+4t, metres where t is time. The work done by the force in 2 seconds is : (1) 12 J (2) 24 J (3) 48 J (4) 64 J 27. In a simple pendulum, the breaking strength of the string is double the weight of the bob. The bob is released from rest when the string is horizontal. The string breaks when it makes an angle  with the vertical– 28. A bob is suspended by a thread of length . The minimum horizontal speed which has t o be imparted to the sphere for it to reach the height of suspension is :- (1) 2 g (2) 2g (3) 2g (4) g 29. A long spring, when stretched by x has a potential energy U. On increasing the length of spring by nx on stretching, the potential energy stored in the spring will be :- 30. A block of mass m moving at speed v collides with another block of mass 3m at rest. The lighter block comes to rest after collision. The coefficient of restitution is :- 31. In a smooth circular tube of radius R, a particle of mass m moving with speed V0 hits another particle of mass 3m at rest as shown. The time after which the next collision takes place (assume elastic collision) :- 32. A block of mass m moving with speed v compresses a spring through distance x before its speed is halved. What is the value of spring constant ? 33. A mass m moving horizontally with velocity  strikes a pendulum of mass m. If the two masses stick together after the collision, then the maximum height reached by the pendulum is : 34. A ball moving with a velocity of 6 m/s strikes an identical stationary ball. After collision each ball moves at an angle of 30° with the original line of motion. What
are the speeds of the balls after the collision ? 35. A stone tied to a string L is whirled in a vertical circle, with the other end of the string at the centre. At a certain instant of time, the stone is as its lowest position and has a speed u. the magnitude of the change in its velocity as it reaches a position where the string is horizontal is : 36. Mass m is released from point A as shown in figure then tension in the string at the point B will be (1) mg (2) 2mg (3) 3mg (4) 4mg 37. A bomb of mass 9 kg explodes into two pieces of masses 3 kg and 6 kg. The velocity of mass 3 kg is 16 m/s. The KE of mass 6 kg (in joule) is (1) 96 (2) 384 (3) 192 (4) 768 38. A body of mass m is accelerated uniformly from rest to a speed v in a time T. The instantaneous power delivered to the body as a function of time is given by:- 39. A rope is used to lower vertically a block of mass M by a distance x with a constant downward acceleration 2 g . The work done by the rope on the block is :- 40. The kinetic energy k of a particle moving along a circle of radius R depends upon the distances as k = as2 . The force acting on the particle is: (Here a is constant) 41. Which of the following statements is correct ? (1) Kinetic energy of a system can be changed without changing its momentum (2) Kinetic energy of a system cannot be changed without changing its momentum. (3) Momentum of a system cannot be changed without changing its kinetic energy (4) Body cannot have energy without having momentum. 42. A body of mass 200 gram is moving along XY plane. Work performed by the force given by ( ) F xi yj = + 2 ˆ ˆ acting on it when the body gets displaced from (0, 0) to (1, 2) will be equal to (1) 3 unit (2) 6 unit (3) 5 unit (4) 1.5 unit 43. A stone is projected vertically up to reach maximum height ‘h’. The ratio of its kinetic energy to potential energy, at a height 4 5 h will be :- (1) 5 : 4 (2) 4 : 5 (3) 1 : 4 (4) 4 : 1 44. Six steel balls of identical size are lined up along a straight frictionless groove. Two similar balls moving with a speed V along the groove collide with this row on the extreme left hand then- (1) all the balls will start moving to the right with speed V/8 each (2) all the six balls initially at rest will move on with speed V/6 each and two identical balls will come to rest (3) two balls from the extreme right end will move on with speed V each and the remaining balls will remain at rest (4) one ball from the right end will move on with speed 2V, the remaining balls will be at rest. 45. Two particles each of mass m travelling with velocities u1 and u2 collide perfectly