What Mass Must the Smaller Ball Have to Prevent the Larger Ball from Bouncing?

[stanwille]

Homework Statement

2 balls fall from a given height. 1 ball is smaller than the other and the mass of the bigger ball is given. The larger ball is directly below the smaller ball when dropped and the separation is distance is negligible. When the larger ball hits the floor, the smaller ball collides with the larger ball. What is the mass of the smaller ball if it prevents the larger ball from bouncing back up (it remains at rest on the floor)?

Homework Equations

Kinetic energy, conservation of energy

The Attempt at a Solution

The mass of the smaller ball is equal to that of the larger ball.
I am not sure of this answer though

 

[Doc Al]

Show how you arrived at this answer. Hint: What's conserved?