# A ball with a mass of # 5 kg# is rolling at #1 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

#### Answer:

The post collisions velocities are

#### Explanation:

Since the collision is elastic, we have conservation of momentum

And conservation of kinetic energy

The mass the first ball is

The velocity of the first ball before the collision is

The mass of the second ball is

The velocity of the second ball before the collision is

The velocity of the first ball after the collision is

The velocity of the second ball after the collision is

Therefore,

Solving for

From equation

Substituting in equation

Therefore,

The first solutions are the initial conditions.

The post collisions velocities are