# Homework Help: Bounce of football (kinetic and potential energy)

1. Nov 7, 2009

### Mcoroklo

1. The problem statement, all variables and given/known data

A football (european) that hits ortogonally a surface will reflect such that the kinetic energy of the ball after the collision will be a fraction of the kinetic energy of the ball before the collision. The football makes a free fall from 50 cm to a floor and jumps to the height of 40 cm. After that the football is kicked into a wall (of the same material as the floor) from 5 meters. The ball hits the wall ortogonally and lands on the floor in the distance a from the wall. Find a.

2. Relevant equations

We assume that 4/5 of the football's energy is conserved in a collision because

U1 = 4/5*U2
where U1 is the potential energy before the collision, U2 after.

3. The attempt at a solution

The ball will have 4/5 of its energy conserved after the collision with the wall. This will make the ball go 4/5 the distance it was shot from, making it reach 4 m.

This might be right, but we suspect it's too easy. The fact the Ekin energi has v2 makes me suspect our current suggestion is wrong. a might also depend on how hard the ball is shot, but the excercise doesn't state any force that makes the ball go to and collide with the wall.

Thanks a lot!! :-)