Question

An object has a mass of `6 kg`. The object's kinetic energy uniformly changes from `120 KJ` to `72 KJ` over `t in [0, 4 s]`. What is the average speed of the object?

Answer 1

Average speed is `177.46` `m/s`.

Explanation:

As one Joule is equal to `1` `kgm^2/s^2` and as such the object's kinetic energy changes from `120,000KJ` to `72000KJ`.

As kinetic energy `KE` is given by `1/2mv^2`, velocity is given by `sqrt((2KE)/m)`

and initial velocity is `sqrt((2xx120000)/6)=sqrt40000=200` `m/s`

and final velocity is `sqrt((2xx72000)/6)=sqrt24000=154.92` `m/s`

and average speed is `(200+154.92)/2=354.92/2=177.46` `m/s`.