M2 energy and work question help.

Hi,

I've done parts i. and ii. however I'm stuck on part iii.

If you have the loss of mechanical energy due to air resistance how do you work out the magnitude of the air resistance on the ball? And then, how do you work out the speed at which the ball lands.

The gain in potential energy is 8.76J.
The loss of mechanical energy due to air resistance is 3.24J.

Thanks

Loss of mechanical energy = work done against air resistance
= maginude of air resistance x distance travelled

How far has it travelled on the way up?

Then it will lose more mechanical energy on the way down.