Posted by **Steve** on Thursday, November 12, 2009 at 9:01pm.

A small ball of mass m is aligned above a larger ball of mass M = 0.79 kg (with a slight separation), and the two are dropped simultaneously from height h = 2.0 m. (Assume the radius of each ball is negligible relative to h).

(a) If the larger ball rebounds elastically from the floor and then the small ball rebounds elastically from the larger ball, what value of m results in the larger ball stopping when it collides with the small ball?

I'm not understanding what it's asking here... I'm assuming that momentum is conserved (even after the big ball bounces) so for the other ball to cause a collision which results in the big ball stopping the mass should be the same because the speeds are going to be equal, but that is not correct.