Mass, weight and gravitational field strength - OCR GatewayGravitational potential energy

When an object is lifted in a gravitational field, energy is transferred to a gravity store. This store is called gravitational potential energy.

gravitational potential energy = mass × height × gravitational field strength (g)

This is when:

• gravitational potential energy is measured in joules (J)
• mass is measured in kilograms (kg)
• height is measured in metres (m)
• gravitational field strength (g) is measured in newtons per kilogram (N/kg)

Example

Calculate the energy transferred to the gravity store when a woman of mass 60 kg climbs 4 rungs up a ladder. Each rung is 15 cm high.

First calculate the distance climbed in metres:

15 cm is 0.15 m

0.15 × 4 = 0.6 m

Then calculate the gravity store increase (the gravitational potential energy), remembering that g is 10 N/kg on Earth:

gravitational potential energy = mass × height × gravitational field strength (g)

gravitational potential energy = 60 × 0.6 × 10

gravitational potential energy = 360 J