Determine the gravitational potential energy, in kJ, of 1 m3 of liquid water at an elevation of 30 m above the surface of Earth. The acceleration of gravity is constant at 9.7 m/s2 and the density of the water is uniform at 1000 kg/m3. Determine the change in gravitational potential energy if the elevation decreases by 10 m.

Explanation:

Gravitational potential energy = mgh where m is mass , g is acceleration due to gravity and h is height from the ground .

In the first case mass m = volume x density

= 1 x 1000 = 1000 kg

height h = 30 m

potential energy = 1000 x 30 x 9.8 = 294000 J = 294 kJ .

When height decreases by 10 m , potential decreases as follows .

Decrease in potential energy

= mass x gravitational energy x decrease in height

= 1000 x 9.8 x 10

= 98000 J

= 98 kJ .

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