# A ball with a mass of #12# #kg# moving at #8# #ms^-1# hits a still ball with a mass of #20# #kg#. If the first ball stops moving, how fast is the second ball moving? How much kinetic energy was lost as heat in the collision?

##### 1 Answer

Initial momentum of

#### Explanation:

Momentum is conserved, so the momentum of the

Rearranging to make velocity the subject:

Now we know the masses and velocities of both objects before an after the collision. Stationary objects have

The total kinetic energy before the collision is given by:

The total kinetic energy after the collision is:

Now, **energy** is conserved, but **kinetic energy** is *not* conserved in an inelastic or partially elastic collision. Some of the kinetic energy is converted into other forms, such as heat. The 'missing' energy in this case is