Question

What is the kinetic energy of an object with a mass of `3 kg` that has been in freefall for `2 s`?

Answer 1

E_k =600 J

Explanation:

from the first movument law
`s= s° + v°t + 1/2 a t^2`
but s°=0 and v° = 0 so
`s= 1/2 a t^2= 1/2 10 m/s^2 (2s)^2 = 20 m`
the kinetic energy is like the potential energy lost
`E_w= mgh = 3kg xx 10 m/s^2 xx 20m = 600 J`
`E_k= 600 J`
otherwise you can have also
`v= at= 10 m/s^2 xx 2 s = 20 m/s`
`E_k =1/2 m xx v^2 = 1/2 xx 3 kg xx (20m/s)^2=600J`