Question

In hydroelectric dams, gravitational potential energy is used to produce electrical energy. What is the mass of water that must fall over a dam that is 12 m high in order to produce the same amount of energy in an AA battery (10,800 J)?

Answer 1

What mass of water must fall 12m in order to lose 10,800J of gravitational potential energy ?

Potential energy = (mass) x (gravity) x (height)

10,800J = (mass) x (9.8 m/s²) x (12m)

Mass = (10,800J) / (9.8 m/s² x 12m)

Mass = (10,800 / 9.8 x 12) (Joule-sec²/m²)

(Units:  Joule-sec²/m² = N-m-sec²/m² = (kg-m/s²)-m-sec²/m² = kg )

Mass = 91.8 kg