Physics-DPP-1-15.work, power and energy

PHYSICS Topic: WORK, POWER & ENERGY Date: 1. Three particles A, B and C are projected from the top of a tower with the same speed. A is thrown straight upwards, B straight down and C horizontally. They hit the ground with speeds vA, vB and vC , then which of the following is correct : (a) vA = vB > vC (b) vA = vB = vC (c) vA > vB = vC (d) vB > vC > vA 2. A body of mass 0.1 kg moving with a velocity of 10 m/s hits a spring (fixed at the other end) of force constant 1000 N/m and comes to rest after compressing the spring. The compression of the spring is : (a) 0.01 m (b) 0.1 m (c) 0.2 m (d) 0.5 m 3. Under the action of a force, a 2 kg body moves such that its position x as a function of time t is given by x = and t in second. The work done by the force in the first two seconds is : (a) 1600 J (b) 160 J (c) 16 J (d) 1.6 J 4. When work done by force by gravity is negative : t3 3 , where x is in metre (a) PE increases (b) KE decreases (c) PE remains constant (d) PE decreases 5. If the linear momentum is increased by 50%, then kinetic energy will be increased by : (a) 50 % (b) 100 % (c) 125 % (d) 25 % 6. An engine develops 10 kW of power. How much time will it take to lift a mass of 200 kg to a height of 40 m: (g = 10 ms–2) (a) 4 s (b) 5 s (c) 8 s (d) 10 s 7. Velocity-time graph of a particle of mass 2 kg moving in a straight line is as shown in figure. Work done by the all the forces on the particle is : (a) 400 J (b) – 400 J (c) – 200 J (d) 200 J 8. A vehicle needs an engine of 7500 W to keep it moving with a constant velocity of 20 m/s on a horizontal surface. The force resisting the motion is : (a) 375 dyne (b) 375 N (c) 1, 50, 000 dyne (d) 1, 50, 000 N 9. A uniform chain of length L and mass M is lying on a smooth table and one third of its length is hanging vertically down over the edge of the table. If g is acceleration due to gravity, the work required to pull the hanging part on the table is : (a) MgL (b) MgL 3 (c) MgL 9 (d) MgL 18 10. An object of mass m is tied to a string of length L and a variable horizontal force is applied on it which start at zero and gradually increases until the string makes an angle θ with the vertical. Work done by the force F is : (a) mgL(1- sin θ) (b) mgL (c) (c) mgL(1- cosθ) (d) mgL(1+ cosθ) PHYSICS Topic: WORK, POWER & ENERGY Date: Answer Key 1. (b) 2. (b) 3. (c) 4. (a) 5. (c) 6. (c) 7. (b) 8. (b) 9. (d) 10. (c)