Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R.
**Assertion A:** Body $P$ having mass $M$ moving with speed $u$ has head-on collision elastically with another body $Q$ having mass $m$ initially at rest. If $m \ll M$, body $Q$ will have a maximum speed equal to $2u$ after collision.
**Reason R:** During elastic collision, the momentum and kinetic energy are both conserved.
In the light of the above statements, choose the most appropriate answer from the options given below:
Answer: (C) Both A and R are correct and R is the correct explanation of A
Using conservation of momentum and kinetic energy for a 1D elastic collision, the speed of the initially resting body is
$$v_Q = \frac{2M}{M+m}\,u$$
For $m \ll M$, $v_Q \to 2u$, its maximum possible value. So A is correct.
This result is obtained precisely from conservation of momentum and kinetic energy, so R is correct and explains A.
Solution by Sreeraj P, M.Sc Physics