# What is the height to which that ball rebounds?

1. Mar 2, 2006

### avb203796

A 90.0 g ball is dropped from a height of 7.0 m straight down. It rebounds to a height of 6.0 m. What is the impulse that the ball receives from the floor? How much kinetic energy is lost because of the collision with the floor? If the collision with the floor is elastic, what is the height to which that ball rebounds? Show formulas/calculations to support your answer.

I have no idea even where to begin with this problem. Could some one maybe give me a hint or two as to how to procede?

2. Mar 2, 2006

### Chi Meson

Solving the second pqart first makes more sense to me.
Compare the maximum potential energies before and after the bounce.

Isn't the third part answered in the question? Is this exactly how it was asked?

3. Mar 2, 2006

### avb203796

This is exactly how it was asked but I checked with my professor and this last part was hypothetical. He was asking what the height of the rebound would have been if the collision with the floor had been elastic?

Having said that how would I find the maximum potential energies from before and after the jump?

4. Mar 3, 2006

### Hootenanny

Staff Emeritus
You need to use the formula for gravitational potential energy ($mgh$). This will give you the inital energy and the energy when it is at its maximum height after the collision. Neglecting air resistance the difference in energy will be the energy lost due to the collision with the floor.

As for the 'hypothetical' question, think about what an elastic collision means.