OBJECTIVE LEVEL - I 1. If the KE of a body becomes four times of its initial value, then the new momentum will be : (a) three times its initial value (b) four times its initial value (c) twice its initial value (d) unchanged. 2. A shell explodes and many pieces fly off in different directions. The following is conserved : (a) Kinetic energy (b) Momentum (c) Neither momentum nor KE (d) Momentum and KE. 3. Which one of the following statement is true : (a) Momentum is conserved in elastic collisions but not in inelastic collision (b) Total KE is conserved in elastic collisions but momentum is not (c) Total KE is not conserved but momentum is conserved in inelastic collision (d) KE and momentum both are conserve in all types of collisions. 4. A bag of mass M hangs by a long thread and a bullet (mass m) comes horizontally with velocity v and gets caught in the bag. Then for the combined system (bag + bullet) : (a) Momentum is mMv/(M+m) (b) KE is (1/2)Mu2 (c) Momentum is mv(M+m) /M (d) KE m2v2/2(M+m). 5. A mass m1 moves with a large velocity. It strikes another mass m2 at rest in a head on collision. It comes back along its path with losser speed after collision. Then : (a) m1 > m2 (b) m1 < m2 (c) m1 = m2 (d) there is no relation between m1 and m2. 6. Choose incorrect one. If no external force acts on a system : (a) Velocity of centre of mass remains constant (b) Velocity of centre of mass is not constant (c) Velocity of centre of mass may be zero (d) Acceleration of centre of mass is zero. 7. Two particle A and B initially at rest, move towards each other under a mutual force speed of A is V and the speed of B is 2V, the speed of the centre of mass of the system is : (a) zero (b) V (c) 1.5V (d) 3V. 8. A ball of mass m moving with a speed u undergoes a head-on elastic collision with a ball of mass nm initially at rest. The fraction of the incident energy transferred to the heavier ball is (a) (c) n 1 n 2n (1 n)2 (b) (d) n (1 n)2 4n (1 n)2 . 9. Two blocks of masses 10 kg and 4 kg are connected by a spring of negligible mass and placed on a frictionless horizontal surface. An impulse gives a velocity of 14 ms-1 to the heavier block in the direction of the lighter block. The velocity of the centre of mass is : (a) 30 ms-1 (b) 20 ms-1 (c) 10 ms-1 (d) 5 ms-1. 10. A body is dropped and observed to bounce a height greater than the dropping height. Then : (a) the collision is elastic (b) there is additional source of energy during collision (c) it is not possible (d) this type of phenomenon does not occur in nature. 11. A rocket works on the principle of conservation of : (a) mass (b) kinetic energy (c) linear momentum (d) angular momentum. 12. Choose the correct definition of impulse : (a) impulse is defined as rate of change of momentum of particle (b) impulse is defined as change in momentum of a particle (c) impulse is defined as the integral of force with respect to time (d) both 2 and 3 are correct.