# Greater momentum than initial?

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?

• Calculate the kinetic energy before and after the collision and see for yourself. May 27, 2015 at 7:19

• So the maximum speed to which the truck can be accelerated by pingpong ball is up to $2p_{ball}/m_{ball}$ ? And if the kinetic energy of the ball is absorbed by the truck then the maximum possible speed to which truck can be accelerated is $p_{ball}/m_{ball} ?$ Maan, I'm so disoriented. Jun 7, 2015 at 9:28
• Isn't $p_{ball}/m_{ball}$ just $v_{ball}$? If the mass of the truck is negligible compared to the mass of the ping pong ball, it will be accelerated by $2v_{ball}$, since it's just this experiment in reverse. That last part isn't right though. How did you calculate it? Jun 9, 2015 at 8:23