A block `'A'` of mass `m_1` hits horizontally the rear side of a spring (ideal) attached to a block `B` of mass `m_(2)` resting on a smooth horizontal surface. After hitting, `'A'` gets attached to the spring.

Some statements are given at any moment of time:
i. If velocity of `A` is greater than `B`, then kinetic energy of the system will be decreasing.
ii. If velocity of `A` is greater than `B`, then kinetic energy of the system will be increasing.
iii. If velocity of `A` is greater than `B`, then momentum of the system will be decreasing.
iv. If velocity of `A` is greater than `B`, then momentum of the system will be increasing.
Now select correct alternative:

Options

A. only iv
B. only i
C. ii and iv
D. i and ii

Answer

B

Explanation

Statement i is correct because in this case, spring would be compressing. So `PE` in the spring will be increasing. It means `KE` of the system will be decreasing as the total mechanicla energy of the system is constant.
Further momentum of the system will always be conserved. it will neithter be increasing nor be decreasing.