Question

If an object with a mass of `2 kg` changes speed from `6 m/s` to `2 m/s`, by how much does its kinetic energy change?

Answer 1

So the kinetic energy was reduced by a factor of `4`. Or, equivalently, the kinetic energy was reduced by `27 "J"`.

Explanation:

Before:

`E_k = 1/2mv_i^2 = 1/2(2)(6)^2 = 36 " J"`

After:

`E_k = 1/2mv_f^2 = 1/2(2)(3)^2 = 9 " J"`

So the kinetic energy was reduced by a factor of `4`. Or, equivalently, the kinetic energy was reduced by `27 "J"`.