Question

A tank has a rectangular base 3 m × 4 m, the vertical sides are 6 m high, and the
depth of the water is 2 m. How much work is required to pump all of the water out over the
side? The density of water is 1000 kg/m3
and gravitational acceleration is 9.8 m/s2
.

Answer 1

Find the mass of the water
3*4*2 * 1000 kg = 24,000 kg

Find the height of the center of mass of the water
1 meter

lift it 6 - 1 = 5 meters

work in = potential gained = m g h = 24,000 * 9.8 * 5 Joules

Answer 2

Now if you think to use a siphon, it takes zero :)