# A model train, with a mass of #3# #kg#, is moving on a circular track with a radius of #3# #m#. If the train's kinetic energy changes from #18# #J# to #0# #J#, by how much will the centripetal force applied by the tracks change by?

##### 1 Answer

The centripetal force is given by

#### Explanation:

The centripetal force on an object of mass

In this case we know the mass is

We can rearrange this to make

Since the kinetic energy at the second time is

At the first time, the kinetic energy is

This means the centripetal force is:

So the centripetal force was