Q: A ball moving with a velocity $\vec{v}$ collides elastically with another ball of equal mass, in a one dimensional collision. Which of the following is not possible ?
(a) First ball will come to rest
(b) Second ball will move with a velocity $\vec{v}$
(c) Both balls will move with velocity $\vec{v}$ after collision
(d) The first ball will move with a velocity less that $\vec{v}$
Ans: (c)