GPE & KE Flashcards

All 6 cards in this deck

What is the equation for the change in gravitational potential energy when an object is raised?

change in GPE (J) = mass (kg) × gravitational field strength (N/kg) × change in vertical height (m)

What is the equation for the kinetic energy of a moving object?

kinetic energy (J) = $\frac{1}{2}$ × mass (kg) × (speed)$^2$ (m/s)

True or false? Doubling the speed of a car doubles its kinetic energy.

False. Kinetic energy is proportional to speed squared, so it becomes four times as great.

What are the steps to find the height an object was raised from its gain in gravitational potential energy?

e.g. a 2 kg mass gains 60 J, $g = 10$ N/kg

1. Write the equation: $\Delta GPE = m g \Delta h$, so $60 = 2 \times 10 \times \Delta h$
2. Rearrange: $\Delta h = 60 \div 20$
3. Height = 3 m

What are the steps to find the speed of an object that has fallen from a height?

e.g. a ball dropped from 5 m, $g = 10$ N/kg

1. GPE lost = KE gained: $mg\Delta h = \frac{1}{2}mv^2$
2. Mass cancels: $v^2 = 2g\Delta h = 2 \times 10 \times 5 = 100$
3. $v = 10$ m/s

What are the steps to find the kinetic energy lost by a vehicle from the braking force and distance?

e.g. a braking force of 500 N acts over 20 m

1. Work done = force × distance = $500 \times 20 = 10\,000$ J
2. Work done by the brakes = kinetic energy lost
3. Kinetic energy lost = 10 000 J