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Conservation of Energy

Energy stores and closed systems

  • 3 things to know
  • Paper 1

Overview

Energy store changes for a thrown ball, a freewheeling cyclist, a crashing car, a hammer, a kettle and a braking car, then what a closed system is and why its total energy stays fixed.

What you need to know

Answer each one before you reveal it.

Your recallNot started
Key term

Describe the change in the way energy is stored as a ball is thrown vertically upwards.

Key term

Describe the main change in energy stores as a cyclist freewheels up a slope and slows down.

Key term

Explain, in terms of energy stores, why a ball thrown upwards is momentarily stationary at its highest point.

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    Describe the change in the way energy is stored as a ball is thrown vertically upwards.

    Model answer

    Energy is transferred from the kinetic store of the ball to its gravitational potential store as it rises.

  2. 2

    Describe the main change in energy stores as a cyclist freewheels up a slope and slows down.

    Model answer

    Energy is transferred from the kinetic store of the cyclist and bicycle to their gravitational potential store.

  3. 3

    Explain, in terms of energy stores, why a ball thrown upwards is momentarily stationary at its highest point.

    Model answer

    At the top the kinetic store has been emptied into the gravitational potential store, so the ball has no speed.

  4. 4

    Describe the energy transfers that take place when a moving car hits a wall and stops.

    Model answer

    The kinetic store of the car empties, and energy is transferred to the thermal stores of the crumpled metal and the air, and as sound.

  5. 5

    Explain why a hammer head becomes warm after it has repeatedly struck a nail.

    Model answer

    Each impact transfers energy from the kinetic store of the hammer to the thermal stores of the hammer, the nail and the wood.

  6. 6

    Describe the change in energy stores when a constant force accelerates a trolley along a level bench.

    Model answer

    The force fills the kinetic store of the trolley, with a small amount transferred to thermal stores by friction.

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Key Concepts of Physics
Motion and Forces
Conservation of Energy
Waves

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ALength is measured in metres, with the symbol m.
BMass is measured in kilograms, symbol kg.
CTime is measured in seconds, symbol s.

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Assemble a full-mark answer from its marking points, in the order an examiner wants them.

Watt means the unit of power, symbol W.
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