Question

If an object with a mass of `7 kg` changes speed from `4ms^-1` to `5 ms^-1`, by how much does its kinetic energy change?

Answer 1

The kinetic energy changes from `56 J` to `87.5 J`, a change of `31.5 J`.

Explanation:

Kinetic energy is given by `E_k = 1/2mv^2`

If the mass, `m`, is `7 kg`, and the velocity, `v`, is `4 ms^-1`, the `E_k` is `56 J`. If the velocity changes to `5 ms^-1` the `E_k` changes to `87.5 J`. Subtracting the former from the latter gives a change of `31.5 J`.