Title 06. WORK ENERGY AND POWER.pdf ✅

PAPER 1 (1.) If only conservative forces are working in the system and we apply some external force (1) Wext = ΔU (always) (2) Wconservative = −ΔU (always) (3) Wext = +  ΔU ΔK E (always) (4) Wconservative = −  ΔK E (2.) The force acting on a body moving along x -axis varies with the position of the particle as shown in the figure. The body is in stable equilibrium at: (1) 1 x x = (2) 2 x x = (3) both 1 x and 2 x (4) neither 1 x nor 2 x . (3.) Two springs of force constant 100 N / m and 150 N / m are in series as shown. The block is pulled by a distance of 2.5 cm to the right from equilibrium position. What is the ratio of work done by the spring at left to the work done by the spring at right. (1) 3 2 (2) 2 3 (3) 0.2 (4) None of these (4.) A uniform rectangular marble slab is 3.4 m long and 2.0 m wide. It has a mass of 180 kg . If it is originally lying on the flat ground, how much work is needed to stand it on an end? (1) 2.0 kJ (2) 3.0 J (3) 3.0 kJ (4) 3000 kJ (5.) A body of mass 3 kg is under a force, which causes a displacement in it is given by 3 S t = /3 (in m ). Find the work done by the force in first 2 seconds (1) 2 J (2) 3.8 J (3) 5.2 J (4) 24 J (6.) When a 1.0 kg mass hangs attached to a spring of length 50 cm , the spring stretches by 2 cm . The mass is pulled down until the length of the spring becomes 60 cm . What is the amount of elastic energy stored in the spring in this condition, if 2 g 10 m / s = : (1) 1.5 Joule (2) 2.0 Joule (3) 2.5 Joule (4) 3.0 Joule.
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(7.) A weight lifter lifts 300 kg from the ground to a height of 2 meter in 3 second. The average power generated by him is : (1) 5880 watt (2) 4410 watt (3) 2205 watt (4) 1960 watt (8.) A truck of mass 30,000 kg moves up an inclined plane of slope 1 in 100 at a speed of 30kmph . The power of the truck is (given 1 g 10 ms− = ) : (1) 25 kW (2) 10 kW (3) 5 kW (4) 2.5 kW (9.) A 60 kg man runs up a staircase in 12 seconds while a 50 kg man runs up the same staircase in 11 , seconds, the ratio of the rate of doing their work is : (1) 6:5 (2) 12:11 (3) 11:10 (4) 10:11 (10.) A pump motor is used to deliver water at a certain rate from a given pipe. To obtain twice as much water from the same pipe in the same time, power of the motor has to be increased to : (1) 16 times (2) 4 times (3) 8 times (4) 2 times (11.) A quarter horse power motor runs at a speed of 600 r.p.m. Assuming 40% efficiency the work done by the motor in one rotation will be : (1) 7.46 J (2) 7400 J (3) 7.46 ergs (4) 74.6 J (12.) A load hangs from a travelling crane, moving horizontally with velocity v . If the load is not to swing more than 4 m horizontally, when the crane is stopped suddenly, what is the maximum allowable speed of the crane : (1) 4.05 m / s (2) 4.00 m / s (3) 3.00 m / s (4) 3.50 m / s (13.) A 10 kg block is pulled in the vertical plane along a frictionless surface in the form of an arc of a circle of radius 10 m . The applied force is of 200 N as shown in figure. If the block had started from rest at A, the velocity at B would be :
(1) 1.7 m / s (2) 17 m / s (3) 27 m / s (4) 34 m / s (14.) A block of mass m is suspended by a light thread from a lift. The lift is moving upward with uniform velocity v . From the frame of lift, the work done by tension on the block in t seconds will be : (1) −mgvt (2) 0 (3) mgvt / 2 (4) mgvt (15.) 300 J of work is done in sliding a 2 kg block up an inclined plane of height 10 m. Taking 2 g =10 m / s , work done against friction is : (1) 100 J (2) zero (3) 1000 J (4) 200 J (16.) A 10 kg mass moves along x -axis. Its acceleration as a function of its position is shown in the figure. What is the total work done on the mass by the force as the mass moves from x = 0 to x = 8 cm : (1) 2 8 10−  joules (2) 2 16 10−  joules (3) 4 4 10−  joules (4) 3 1.6 10−  joules. (17.) A particle moves under the effect of a force F Cx = from x = 0 to 1 x x = . The work done in the process is : (1) 2 Cx1 (2) 2 1 1 Cx 2 x (3) Cx1 (4) Zero