# Kinetic Energy Question

## Homework Statement

A ball of mass 0.8kg moving initially at 8.0m/s has a head on collision with a 0.4kg ball that is at rest. If the collision is perfectly elastic, what is the velocity of each ball after the collision?

Ek=(mv2)/2

## The Attempt at a Solution

I found the kinetic energy of the first ball, then split the knietic energy between the two balls after the collision to individually find the velocity of each.

## Answers and Replies

Doc Al
Mentor
I found the kinetic energy of the first ball, then split the knietic energy between the two balls after the collision to individually find the velocity of each.
What do you mean by 'split the kinetic energy'?

Hint: What else is conserved during the collision besides energy?

What do you mean by 'split the kinetic energy'?

Hint: What else is conserved during the collision besides energy?

I divided the total kinetic energy by two... and is momentum the answer to your question

Doc Al
Mentor
I divided the total kinetic energy by two...
You cannot assume that the kinetic energy divides equally.
and is momentum the answer to your question
Yes. Use conservation of momentum and energy to solve for the final speeds.

You cannot assume that the kinetic energy divides equally.

Yes. Use conservation of momentum and energy to solve for the final speeds.

How do I do that?

Doc Al
Mentor
How do I do that?
Write equations for energy conservation and momentum conservation, then solve them.