A bucket of water of mass 30 kg is pulled at a constant velocity up to a platform 30 meters above the ground.

Question

A bucket of water of mass 30 kg is pulled at a constant velocity up to a platform 30 meters above the ground. This takes 18 minutes, during which time 2 kg of water drips out at a steady rate through a hole in the bottom. Find the work needed to raise the bucket to the platform. (Use g=9.8 m/s^2)

Answer 1

Work = force x distance. Distance is 30 meters

The force needed is the force to overcome force of gravity (constant velocity so net force is 0).

Force of gravity = mg. However we are losing mass as we go at a constant rate so we need to use the average mass. Initial mass is 30, final is 28, so average is (30+28)/2=29kg

Plug in values:

Fg=29*9.81= 284.49

Work = 284.49 * 30 = 8534.7N