posted by Mark .
Can someone check and advise on this
potential energy of 2 tonne of water held 120m above a flood plain by a dam.
potential energy = 2032 kg (2 Tonne) x 9.81 ms x 120m
pe = 2392070.4 Joules
Convert to kilojoules
2392070.4 / 1000
pe = 2392 kJ (To four significant figures)
You measured the height to the top of the dam, that is not where the water is. I recommend you go to the center of the dam, if you assume the cg of the water held is there. Usually, because of sloping bottom, the cg is about at the sixty percent height, but that depends on the geology of the bottom. Assume average depth of the water at 60m.
Then, PE= mgh as you did
Also, I am not certain where you got the 2032kg per 2 metric tons. I always used 1000kg is a metric ton.
I had assumed a uk tonne at 1016 kg