Question

What is the kinetic energy of an object with a mass of `1 kg` that has been in freefall for `4 s`?

Answer 1

`approx 800J`

Explanation:

Given that it has been falling free for 4 seconds from rest we can use the equation:

`v=u+at`
`a=9.81 ms^-2`
`u=0`
`t=4 s`

Hence
`v=39.24 ms^-1`

Now using the kinetic energy equation:

`E_k=(1/2)mv^2`
`E_k=(0.5) times 1 times (39.24)^2`
`E_k=769.8 approx 800J` as we only had 1 significant figure in the question we should answer to 1 significant figure.