# A ball with a mass of # 5 kg# is rolling at #7 m/s# and elastically collides with a resting ball with a mass of #4 kg#. What are the post-collision velocities of the balls?

##### 1 Answer

Jan 6, 2016

I found:

#### Explanation:

We can use conservation of momentum

So:

Being an elastic collision also kinetic energy

So:

We can use the two equations together and we get:

From the first equation:

Substitute into the second and get:

Corresponding to: