Newton's Laws

This is a conservation of energy question. The event is the collision. The initial energy can be calculated by gravitational potential energy:

The final total energy must be the same. The energy of the scattered pieces must add to

The answer to this question lies within Newton's third law: for every action, there is an equal and opposite reaction. If the large ball applies a force on the smaller ball, the smaller ball will apply a force on the large ball in the opposite (negative) direction.