Title 6.WORK ENERGY AND POWER - Questions.pdf ✅

6.WORK ENERGY AND POWER (1.)Figure shows the F-x graph. Where F is the force applied and x is the distance covered By the body along a straight line path. Given that F is in newton and x in metre, what is the work done? (a.) 10 J (b.) 20 J (c.) 30 J (d.) 40 J (2.)A car of mass 1250 kg is moving at 30 m/s. Its engine delivers 30 kW while resistive force due to surface is 750 N. What max acceleration can be given in the car (a.) 1 3 m/s 2 (b.) 1 4 m/s 2 (c.) 1 5 m/s 2 (d.) 1 6 m/s 2 (3.)The potential energy of a certain spring when stretched through a distance ‘S’ is 10 joule. The amount of work (in joule) that must be done on this spring to stretch it through an additional distance ‘S’ will be (a.) 30 (b.) 40 (c.) 10 (d.) 20 (4.)An automobile weighing 1200 kg climbs up a hill that rises 1 m in 20 s. Neglecting frictional effects. The minimum power developed by the engine is 9000 W. If g = 10ms −2 , then the velocity of the automobile is (a.) 36 km h −1 (b. ) 54 km h −1 (c.) 72 km h −1 (d. ) 90 km h −1 (5.)A particle moves in a straight line with retardation proportional to its displacement. Its loss of KE for any displacement x is proportional to (a.) x (b.) x 2 (c.) x 0 (d.) e x (6.)10 L of water per second is lifted from well through 20 m and delivered with a velocity of 10ms −1 ,then the power of the motor is (a.) 1.5 Kw (b.) 2.5 Kw (c.) 3.5 Kw (d.) 4.5 Kw (7.)Statement I In an elastic collision between two bodies, the relative speed of the bodies after collision is equal to the relative speed before the collision. Statement II Inan elastic collision, the linear momentum of the system is conserved. (a.) Statement I is true ,statement II is true; statement II is a correct explanation for statement I (b.) Statement I is true, Statement II is true; statement II is not correct explanation for statement I (c.) Statement I is true, Statement II is false (d.) Statement I is false, Statement II is True (8.)A body of mass 2 kg is moving with velocity 10 m/s towards east. Another body of same mass and same velocity moving towards north collides with former and coalesces and moves towards north-east. Its velocity is (a.) 10 m/s (b.) 5 m/s (c.) 2.5 m/s (d.) 5√2 m/s (9.)A ball of mass m moves with speed v and strikes a wall having infinite mass and it returns with same speed then the work done by the ball on the wall is (a.) Zero (b.) mv J (c.) m/v.J (d.) v/m J (10.)Identify the wrong statement (a.) A body can have momentum without energy (b.) A body can have energy without momentum (c.) The momentum is conserved in an elastic collision (d.) Kinetic energy is not conserved in an inelastic collision (11.)Velocity-time graph of a particle of mass 2 kg moving in a straight line is as shown in figure. Work done by all forces on the particle is 10 5 0 –5 –10 1 2 3 4 x F
(a.) 400 J (b.) −400 J (c.) −200 J (d.) 200 J (12.)The slope of the kinetic energy versus position vector gives the rate of change of (a.) Momentum (b.) Velocity (c.) Force (d.) Power (13.)Consider elastic collision of a particle of mass m moving with a velocity u with another particle of the same mass at rest. After the collision the projectile and the struck particle move in directions making angles θ1 and θ2 respectively with the initial direction of motion. The sum of the angles θ1 + θ2, is (a.) 45° (b.) 90° (c.) 135° (d.) 180° (14.)A particle of mass M starting from rest undergoes uniform acceleration. If the speed acquired in time T is V, the power delivered to the particle is (a.) MV 2 T (b.) 1 2 MV 2 T2 (c.) MV 2 T2 (d.) 1 2 MV 2 T (15.)Which of the following is not a conservative force (a.) Gravitational force (b.) Electrostatic force between two charges (c.) Magnetic force between two magnetic dipoles (d.) Frictional force (16.)A body moves from a position r1= (2î-3ĵ-4k̂ ) m to a position, r2= (3î-43ĵ-5k̂) m under the influence of a constant force F= (4î− 4ĵ+ 5k̂ ) N. The work done by the force is (a.) 57 J (b.) 58 J (c.) 59 J (d.) 60 J (17.)A neutron travelling with a velocity v and K.E. E collides perfectly elastically head on with the nucleus of an atom of mass number A at rest. The fraction of total energy retained by neutron is (a.) ( A−1 A+1 ) 2 (b.) ( A+1 A−1 ) 2 (c.) ( A−1 A ) 2 (d.) ( A+1 A ) 2 (18.)A man, by working a hand pump fixed to a well, pumps out 10 m3 water in 1 s. If the water in the well is 10 m below the ground level, then the work done by the man is (g = 10ms −2 ) (a.) 103 J (b.) 104 J (c.) 105 J (d.) 106 J (19.)A force–time graph for a linear motion is shown in figure where the segments are circular. The linear momentum gained between zero and 8 second is (a.) −2π newton × second (b.) Zero newton × second (c.) +4π newton × second (d.) −6π newton × second (20.)A 2.0 kg block is dropped from a height of 40 cm onto a spring of spring constant k = 1960 Nm−1 . Find the maximum distance the spring is compressed (a.) 0.080 m (b.) 0.20 m (c.) 0.40 m (d.) 0.10 m (21.)In which of the following cases, can the work done increase the potential energy? (a.) Both conservative and non-conservative forces (b.) Conservative force only (c.) Non- conservative force only (d.) Neither conservative nor conservative forces (22.)A rifle bullet loses 1/20th of its velocity in passing through a plank. The least number of such planks required just to stop the bullet is (a.) 5 (b.) 10 (c.) 11 (d.) 20 (23.)The work done in pulling up a block of wood weighing 2 kN for a length of 10 m on a smooth 2 4 6 8 –2 +2 Force (newtons) Time
plane inclined at an angle of 15° with the horizontal is [sin15° = 0.2588] (a.) 4.36 kJ (b.) 5.17 kJ (c.) 8.91 kJ (d.) 9.82 kJ (24.)The kinetic energy acquired by a body of mass m in travelling some distance s, starting from rest under the action of a constant force, is directly proportional to (a.) m° (b.) m (c.) m2 (d.) √m (25.)A body is moving with velocity v, breaks up into two equal parts. One of the part retraces back with velocity v. Then the velocity of the other part is (a.) v in forward direction (b.) 3v in forward direction (c.) v in backward direction (d.) 3v in backward direction (26.)A nucleus at rest splits into two nuclear parts having same density and radii in the ratio 1:2. Their velocities are in the ratio (a.) 2: 1 (b.) 4: 1 (c.) 6: 1 (d.) 8: 1 (27.)In an elastic collision of two particles the following is conserved (a.) Momentum of each particle (b.) Speed of each particle (c.) Kinetic energy of each particle (d.) Total kinetic energy of both the particles (28.)Two spheres A and B of masses m1and m2 respectively collide. A is at rest initially and B is moving with velocity v along x-axis. After collision B has a velocity V 2 in a direction perpendicular to the original direction. The mass A moves after collision in the direction (a.) Same as that of B (b.) Opposite to that of B (c.) θ = tan−1 (1/2) to the x-axis (d.) θ = tan−1 (−1/2) to the x-axis (29.)A U 238 nucleus decays by emitting an alpha particle of speed v ms −1 . The recoil speed of the residual nucleus is (in ms −1 ) (a.) −4v/234 (b.) v/4 (c.) −4v/238 (d.) 4v/238 (30.)4m3of water is to be pumped to a height of 20m and forced into a reservoir at a pressure of 2 × 105 Nm−2 The work done by the motor is (external pressure= 105Nm−2 ) (a.) 8 × 105 J (b.) 16 × 105 J (c.) 12 × 105 J (d.) 32 × 105 J (31.)A gun of mass 20 kg has bullet of mass 0.1 kg in it. The gun is free to recoil 804 J of recoil energy are released on firing the gun. The speed of bullet (ms −1 ) is (a.) √804 × 2010 (b.) √ 2010 804 (c.) √ 804 2010 (d.) √804 × 4 × 103 (32.)A ball dropped from a height of 2m rebounds to a height of 1.5 m after hitting the ground. Then the percentage of energy lost is (a.) 25 (b.) 30 (c.) 50 (d.) 100 (33.)A body of mass 50 kg is projected vertically upwards with velocity of 100 m/sec. 5 seconds after this body breaks into 20 kg and 30 kg. If 20 kg piece travels upwards with 150 m/sec, then the velocity of the block will be (a.) 15 m/sec downwards (b.) 15 m/sec upwards (c.) 51 m/sec downwards (d.) 51 m/sec upwards (34.)At a certain instant, a body of mass 0.4 kg has a velocity of (8î+ 6ĵ)ms −1 . The kinetic energy of the body is (a.) 10 J (b.) 40 J (c.) 20 J (d.) None of these (35.)The momentum of a body increases by 20%. The percentage increase in its kinetic energy is (a.) 20 (b.) 44 (c.) 66 (d.) 88 (36.)A particle is released from a height S. At certain height its kinetic energy is three times its potential energy. The height and speed of the particle at that instant are respectively (a.) S 4 , 3gS 2 (b.) S 4 , √3gS 2
(c.) S 2 , √3gS 2 (d.) S 4 . √3gS 2 (37.)A particle moves along the x−axis from x= x1 to x = x2 under the action of a force given by F=2x. Then the work done in the process is (a.) Zero (b.) x2 2 − x1 2 (c.) 2x2(x2 − x1) (d.) 2x1(x1 − x2) (38.)Which of the following is a unit of energy (a.) Unit (b.) Watt (c.) Horse Power (d.) None (39.)A body of mass m is rest. Another body of same mass moving with velocity v makes head on elastic collision with the first body. After collision the first body starts to moves with velocity (a.) v (b.) Remain at rest (c.) 2v (d.) Not predictable (40.)A neutron having mass of 1.67 × 10−27 kg and moving at 108m/s collides with a deutron at rest and sticks to it. If the mass of the deutron is 3.34 × 10−27 kg then the speed of the combination is (a.) 2.56 × 103 m/s (b.) 2.98 × 105 m/s (c.) 3.33 × 107 m/s (d.) 5.01 × 109 m/s (41.)A man does a given amount of work in 10 sec. Another man does the same amount of work in 20 sec. The ratio of the output power of first man to the second man is (a.) 1 (b.) 1/2 (c.) 2/1 (d.) None of these (42.)From a building two balls A to B are thrown such that A is thrown upwards and B downwards (both vertically). If vA and vB are their respective velocities on reaching the ground, then (a.) vB > vA (b.) vB = vA (c.) vA > vB (d.) Their velocities depends on their masses (43.)A point mass of 1 kg collides elastically with a stationary point mass of 5 kg. After their collision, the 1 kg mass reverses its direction and moves with a speed of 2 ms −1 . Which of the following statements(s) is/are correct for the system of these two masses? (a.) Total momentum of the system is 3 kg − ms −1 (b.) Momentum of 5 kg mass after collision is 4 kg − ms −1 (c.) Kinetic energy of the centre of mass is 0.75 j (d.) Total kinetic energy of the system is 4 j (44.)If the water falls from a dam into a turbine wheel 19.6 m below, then the velocity of water at the turbine is (g = 9.8 m/s 2 ) (a.) 9.8 m/s (b.) 19.6 m/s (c.) 39.2 m/s (d.) 98.0 m/s (45.)If we throw a body upwards with velocity of 4 m/s, at what height does its kinetic energy reduce to half of the initial value (Taking g = 10 ms −1 ) (a.) 4 m (b.) 2 m (c.) 1 m (d.) 0.4 m (46.)A body of mass 10 kg is moving on a horizontal surface by applying a force of 10 N in forward direction. If body moves with constant velocity, the work done by force of fiction for a displacement of 2m is (a.) −20 J (b.) 10 J (c.) 20 J (d.) −5 J (47.)In which case does the potential energy decrease (a.) On compressing a spring (b.) On stretching a spring (c.) On moving a body against gravitational force (d.) On the rising of an air bubble in water (48.)A box is moved along a straight line by a machine delivering constant power. The distance moved by the body in time t is proportional to (a.) 1 1/2 (b.) t 3/4 (c.) t 3/2 (d.) t 2 (49.)A bob of mass m accelerates uniformly from rest to v1 in time t1. As a function of t, the instantaneous power delivered to the body is (a.) mv1t t2 (b.) mv1t t1 (c.) mv1t 2 t1 (d.) mv1 2 t t1 2 (50.)A box of mass 50 kg is pulled up on an incline 12 m long and 2 m high by a constant force of 100 N from rest. It acquires a velocity of 2 ms −1 on