The question is :
Heavier object A, initially at rest, is struck by lighter object B. Is it possible for object A to have a larger final momentum than the initial momentum of object B?
The answers is yes and the argument as follows: Suppose a pingpong bouncing back upon hitting a stationary truck. The change in momentum of the ball is $ 2mv$. Conservation of momentum then requires the more massive object to have a momentum $2mv $ in the opposite direction.
But how is it possible? After the collision the ball retains same kinetic energy while granting some of it to the truck? Isn't it violation of the law of conservation of energy?