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Conservation of Energy

Gravitational potential and kinetic energy

  • 3 things to know
  • Paper 5

Overview

Change in gravitational potential energy = mass × gravitational field strength × change in vertical height, finding energy, height and mass, why only vertical height counts, kinetic energy = ½ × mass × (speed)², and speed after a fall.

What you need to know

Answer each one before you reveal it.

Your recallNot started
Numbers

State the equation used to calculate the change in gravitational potential energy of an object that is raised above the ground.

Evaluation

Give the unit of gravitational field strength used in the gravitational potential energy equation.

Numbers

Calculate the gain in gravitational potential energy when a 2 kg bag is lifted 3 m, taking gravitational field strength as 10 N/kg.

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    State the equation used to calculate the change in gravitational potential energy of an object that is raised above the ground.

    Model answer

    Change in gravitational potential energy = mass × gravitational field strength × change in vertical height.

  2. 2

    Give the unit of gravitational field strength used in the gravitational potential energy equation.

    Model answer

    newtons per kilogram, N/kg.

  3. 3

    Calculate the gain in gravitational potential energy when a 2 kg bag is lifted 3 m, taking gravitational field strength as 10 N/kg.

    Model answer

    ΔGPE = 2 × 10 × 3 = 60 J.

  4. 4

    A 30 kg child gains 900 J of gravitational potential energy climbing a ladder. Calculate the vertical height climbed, taking gravitational field strength as 10 N/kg.

    Model answer

    Height = 900 ÷ (30 × 10) = 3 m.

  5. 5

    A crate gains 1500 J of gravitational potential energy when it is raised 5 m. Calculate its mass, taking gravitational field strength as 10 N/kg.

    Model answer

    Mass = 1500 ÷ (10 × 5) = 30 kg.

  6. 6

    Explain why only the vertical height, and not the distance travelled along a ramp, is used to calculate a change in gravitational potential energy.

    Model answer

    Gravitational potential energy depends on how far the object is raised against gravity, which is the vertical height.

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