Question

If an object with a mass of `2 kg` changes speed from `9m/s` to `4 m/s`, by how much does its kinetic energy change?

Answer 1

`-65"J"`

Explanation:

The formula for kinetic energy is given by

`"KE" = 1/2 m v^2`

Initially, the kinetic energy is

`"KE"_"i" = 1/2 (2 "kg")(9 "m/s")^2`

`= 81 "J"`

In the end, the kinetic energy is

`"KE"_"f" = 1/2 (2 "kg")(4 "m/s")^2`

`= 16 "J"`

The change in kinetic energy is given by

`Delta "KE" = "KE"_"f" -` `"KE"_i`

`= 16 "J" - 81 "J"`

`= -65 "J"`