Question

What is the kinetic energy of an object with a mass of `15 kg` that has been in freefall for `7 s`?

Answer 1

Assuming the object was stationary at the beginning of the 7 seconds, its velocity will be `68.6` `ms^-1` leading to a kinetic energy: `E_k` = `1/2mv^2 = 1/2*15*68.6^2=35,294.7 J=35.3 kJ`

Explanation:

Assuming that the initial velocity at `t=0` `s` is `u=0` `ms^-1`, the velocity, `v`, after `7` `s` will be:

`v=u+at=0+9.8*7=68.6` `ms^-1`

For an object of mass `m=15` `kg`, the kinetic energy is then given by:

`E_k=1/2mv^2=1/2*15*68.6^2=35,294.7 J=35.3 kJ`