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1, , KK’s TUITION CENTRE, MEDICAL AND ENGINEERING PHYSICS, FORTNIGHTLY TEST - 4, (Work, Power & Energy), , Attempt all questions and each question carries 4marks., Each wrong answer carries (-1) mark., , FM_- 120, Time 40 min, . Arifle bullet losses 1/20 of its velocity on passing a plank. The least number of planks required just, to stop the bullet is, a 5, b. 7, ec Il, d, 20, , . A force acts on a 3g particle in such a way that the position of the particle as a function of time is, given by x = 31-441? where x is in metre and t in second. The w.d. after 4s is, a S76mJ, b. 450m), c. 490m), d. 530mJ, . Work done ag when it expands from 50 litre to 150 litre at a constant pressure of 2 atmosphere is, a, 2x1, b. 2* 109. Ans:[, c. 2 10°)., do 2x 10°), , . A machine which is 75% efficient uses 12J energy in lifting up [kg mass through a certain height., The mass is allowed to fall through that height. The velocity at the end of its fall is, , a. ¥24m's, b. Vi2 ms, c VIB ms, d. ¥19 ms, , . A body of mass Sm initially at rest explodes into 3 fragments with mass ratio 3:1:1, ‘T'wo fragments, cach of mass m are found to move with a speed of 60 m/s in mutually perpendicular directions. The, velocity of third fragment is, , a. 60V2 mis, b. 202 mis, c. 10V2 mis, d. 6v2 mis, . Two bodies A and B having masses in the ratio 3:1 possess the same kinetic. The ratio of linear momentum of, BtoAis, a 13, b. 3:1. Ans:[ ], e. Lv3, , V31, , a

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0, , 11., , 12., , 2, , A ball of mass m moving with a constant velocity strikes against a ball of same mass at rest. If ¢ is coefficient, of restitution, then the ratio of velocity of 1“ ball to the 2™ ball after collision will be, , i-e, , ive, , e-1 ., , bs Ans:| |, , ite, , i-e, , c., , a, , el, A mass m is moving with velocities v, collides inelastically with a bob of simple pendulum of mass m and get, , embedded into it. The total height to which the masses will rise after collision is, v, , a. ay, , =, 49, =, 29, , b Ans:[ J, , ¢., , 2, a, A car of mass 1000 kg moves at a constant speed of 20 m/s up an incline. Assume that the frictional force is, 200N and that sinO= 1/20 where 6 is the angle of the incline to the horizontal. Taking g = 10 mis’, the power, developed by the engine is, a I4KW, b 4kW, c. 1OKW, d 28KW “4, A particle is accelerating uniformly from rest has velocity v at time t), The work done in time t is, , : +(me) 2, a oe tt,, , d, , , , , , Ans:[, , , , , , , , 2, 1 (mr, lia, 2Xe,, , ay?, 6 =) e, th, , PS, , a @&e, Under the action of force, a 2 kg body moves such that the position x as a function of time is given by x = 3, where x is in metres and t in seconds. The work done by force in the first 2 seconds is, , a. 1600), , b. 16), , « 16 Ans:[ |, , a ou, A metallic wire of length L metre extends by | metre when stretched by suspending a weight Mg from it. The, mechanical energy stored in the wire ts,, , a. 2Mgl, b. Mel Ans:[ J, ec. Mgl2, ds Mgl/4, , Ans:[ |

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3, , 13. A small body is projected in the direction inclined at 45° to the horizontal with K.E. °K’. At the top of its, flight, tts K-E. will be, a. Zero, b KA, ce. Kid Ans:[ |, 4. KW2, 14. A body moves a distance of 10m along a straight line under the action of a force of 5N. If the w.d. is 25J, the, angle which the force makes with the direction of motion is, a, b. 30° Ans:[ ], c. 60°, d 90°, 15. A wire suspended vertically from one of its ends is stretched by attaching a weight of 200 N to the lower end, The weight stretches the wire by [mm. the elastic energy stored in the wire is, a, 10), b. 20) Ans:{ J, c. ON, d 04, 16. A spring of spring constant $x 10°N/m is stretched initially by 5 cm from the unstretched position Then the, work required to stretch it further by another 5 cm is, , , , , , , , , , a. 18.75), b 25) Ans:{ |, c. 625), d 12.5), 17_ A ball is dropped from a height h. If the coefficient of restitution be ‘e’, then to what height will it rise after, Jumping twice from the ground?, a, ch/2, b. 2eh Ans:[ ], c. eh, dich, 18. In figure, a carriage P is pulled up from A to B. The relevant coefficient of friction is 0 4. The work done will, be & a, a, 10KJ re 4| _, b. 23K) . me peg, ce. 25KJ % Ans:[, d= 28K, , 19. A ball of mass m is dropped from a height h on a platform (massless) fixed at the top of a vertical spring as in, figure. The platform is depressed by a distance x. the spring constant is, , , , , , , , , , 2mgh, a Oz, b 28 oe Ans:[ J, x, 2mp(h+x) 2 —, c = x) “X., d zmethex), , n?

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21, , 22, , 23., , 24,, , 25,, , 26., , 4, , |. A bullet of mass 0.01 kg and travelling at a speed of 500 m/s strikes a block of mass 2 kg which is suspended, , by a string of length 5m. The C.G. of the block rises a vertical distance of 0.1m. The speed with which the, bullet cmerges from the block is, , a 110m/s, , b. 220 mis, , ec. 55 m/s Ans:| |, , d. 440 mis, A car is moving along a straight horizontal road with speed v. The coefficient of friction between the tyres and, the road 1s 4. The shortest distance in which the car can be stopped is, , b= Ans:[ J, , A body falling from a height of 10m rebounds from the hard floor. If it loses 20% of its energy in the impact,, the height to which it will rise is, , a. 10m, , b. &m, , c. 7.5m Ans:[ |, , ds 6m, The W.D. by a force F= (- 6x°)t N ts displacing a particle from x ~ 4m to x= -2m is, , a. 360), , bh 240) Ans:[ ], c, -240), d -360), , , , Two springs have their force constant as K; and K»(K:> K)., When they are stretched by the same force, , 2. No work is done in case of both the springs., , b. Equal work is done in case of both the springs., , ¢. More work is done in case of the second spring,, , d. More work is done in case of the first spring., The particle initially at rest on a frictionless surface is acted upon by a horizontal force which is constant in, magnitude and direction. A graph is plotted of the work done on the particle w against the speed of the, particle v, the graph looks like, , a b)] ~ | q)) +, , F=kx =>x=F/k, Wek =%kP'/R, W 1/k since F is constant, , , , , , , , , , , , , , , , , , , , , , , , , , , , A stationary particle explodes into two particles of masses m, and m, which move in opposite directions with, velocities v; and v, . The ratio E,/E; is, , a. miwe/ m4, , b. m/m, , c. mi/ms, , do 1

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27., , 28,, , 29., , 5, , A mass of 0.5kg moving with a speed of 1.5m/s on a horizontal smooth surface, collides nearly weightless, spring of force constant K= SON/m, The maximum compression of the spring would be, , a. 0.5m, , b. 0,15m, , c. 0.12m, , d. 15m, A body of mass m moving with velocity v makes a head on elastic collision with another body of mass 2m, which is initially at rest. The loss of kinetic energy of the colliding body of mass m is, , 2, % ofinitial kinetic energy, , b. 1/9 of initial kinetic energy, , c. 8/9 of initial kinetic energy, , d. % of initial kinetic energy, A motor drives a body along a straight line with a constant force. The power P developed by the motor must, vary with time t according to, , a | | i al + d)|, J / o, , , , , , , , , , , , , , , , , , , , . 10 litres of water per second is lifted from a well through 10m and delivered with a velocity of 10m/s. If, , g=10m/s, then the power of motor is, a. 1kW, b. 15kW, c. 2kW, d. 2.5kW, , seaereeeeee