# A ball with a mass of #7# #kg# moving at #14# #ms^-1# hits a still ball with a mass of #15# #kg#. If the first ball stops moving, how fast is the second ball moving?

##### 1 Answer

Mar 13, 2016

Momentum is conserved, so the momentum after the collision is the same as the total momentum before. This means the final velocity of the

#### Explanation:

Let's call the

Momentum before the collision:

Momentum after the collision:

But conservation tells is this is equal to the total momentum before, so:

Rearranging,

(PS Hi, fellow Queenslander! I taught at UQ in St Lucia for 6 years, but now teach at Griffith on the Gold Coast)