Question

A model train, with a mass of `2 kg`, is moving on a circular track with a radius of `4 m`. If the train's kinetic energy changes from `16 j` to `0 j`, by how much will the centripetal force applied by the tracks change by?

Answer 1

`8` Newtons

Explanation:

We can use kinetic energy formula to get the speed of the train before and after the kinetic energy change:

`v=sqrt((2E)/m)`
`-> v = sqrt((2*16)/2)=sqrt(16)=4`

So we know the train was travelling at `4 ms^-1`

The kinetic energy at the end is `0J` so the train has obviously came to rest.

The centripetal force required at `4ms^-1`:

`F = (mv^2)/r`
`-> F =(2*(4^2))/4=8N`

And the centripetal force required when the train is at rest is just `0N`. Thus the change in change in centripetal force is `8-0=8N`