General
✓✗A simple pendulum is released from one extreme position. At the lowest point its
- speed is zero
- kinetic energy is zero
- potential energy is maximum
- kinetic energy is maximum
General
✓✗Sand falls vertically at a rate of 2 kg/s onto a conveyor belt moving horizontally at 3 m s−1. The power needed to keep the belt moving at constant speed is
- 6 W
- 18 W
- 36 W
- 9 W
General
✓✗A particle on a string of length l has speed \( \sqrt{4gl} \) at the lowest point of a vertical circle. The height above the lowest point at which the string becomes slack is
- \( \dfrac{3l}{2} \)
- \( \dfrac{5l}{3} \)
- 2l
- \( \dfrac{4l}{3} \)
General
✓✗The gravitational potential energy of a body of mass m at a small height h above the ground (taking the ground as zero) is
- mgh
- mh/g
- \( \dfrac12mgh \)
- mg/h
General
✓✗A force of 10 N stretches a spring by 5 cm. The spring constant is
- 500 N/m
- 200 N/m
- 50 N/m
- 2 N/m
General
✓✗A lift of mass 800 kg carrying a load of 400 kg moves up at a constant 2 m s−1. If friction is 2000 N, the power required is (g = 10 m s−2)
- 14 kW
- 24 kW
- 4 kW
- 28 kW
General
✓✗A 60 kg athlete runs up a 15 m high flight of stairs in 15 s. Her power is (g = 10 m s−2)
- 900 W
- 600 W
- 150 W
- 60 W
General
✓✗A force F = 3t2 N (t in s) acts on a 1 kg body initially at rest, along its line of motion. The power delivered at t = 2 s is
- 192 W
- 96 W
- 48 W
- 24 W
General
✓✗A man of mass 60 kg climbs 10 m up a staircase in 20 s. His average power is (g = 10 m s−2)
- 120 W
- 300 W
- 6000 W
- 600 W
General
✓✗A ball is thrown vertically downwards from a height of 20 m with an initial velocity v0. It collides with the ground, loses 50% of its energy in the collision and rebounds to the same height. The initial velocity v0 is (take g = 10 m s−2)
- 20 m s−1
- 28 m s−1
- 10 m s−1
- 14 m s−1
General
✓✗A car of mass 1200 kg moves at a constant speed of 20 m s−1 on a level road against a resistance of 600 N. The power of the engine is
- 24 kW
- 6 kW
- 12 kW
- 30 kW
General
✓✗Which of the following statements about a conservative force is incorrect?
- The work done by it depends on the path
- It can be written as the negative gradient of a potential energy
- The work done by it round a closed path is zero
- Mechanical energy is conserved when only such forces do work
General
✓✗A body of mass 2 kg is thrown vertically up with kinetic energy 490 J. The height at which its kinetic energy becomes half is (g = 9.8 m s−2)
- 12.5 m
- 50 m
- 25 m
- 10 m
General
✓✗Two particles of masses m1 and m2 move with initial velocities u1 and u2. On collision, one of the particles gets excited to a higher level after absorbing energy ε. If the final velocities of the particles are v1 and v2, then we must have
- \( \tfrac12m_1u_1^2 + \tfrac12m_2u_2^2 - \varepsilon = \tfrac12m_1v_1^2 + \tfrac12m_2v_2^2 \)
- \( \tfrac12m_1^2u_1^2 + \tfrac12m_2^2u_2^2 + \varepsilon = \tfrac12m_1^2v_1^2 + \tfrac12m_2^2v_2^2 \)
- \( \tfrac12m_1u_1^2 + \tfrac12m_2u_2^2 = \tfrac12m_1v_1^2 + \tfrac12m_2v_2^2 - \varepsilon \)
- \( m_1^2u_1 + m_2^2u_2 - \varepsilon = m_1^2v_1 + m_2^2v_2 \)
General
✓✗The coefficient of restitution of a collision lies between
- 0 and 1
- 0 and \( \infty \)
- 1 and 2
- −1 and 0