Work, energy and power

Work of a force, kinetic and potential energy, mechanical power and their calculation.

The outline, topic by topic

Each topic is weighted the way the exam weighs it.

Work: what is it?
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Energy transferred by a force moving its point of application: W = F × d × cos θ, in joules.
θ is the angle between the force and the displacement: a force perpendicular to the displacement, or a load held still, does no mechanical work.
A pole vaulter runs fast and then rises high. Which energy transformation?
- Kinetic into potential energy
- Potential into kinetic energy
- Potential into elastic energy
- Thermal into kinetic energy
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Kinetic into potential energy
The bent pole stores the run-up's kinetic energy as elastic energy, then gives it back as height.
Kinetic energy: what is it?
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Energy of motion: KE = ½ × m × v².
Doubling speed quadruples the energy.
Why does run-up speed matter so much in pole vault?
- The available energy grows in proportion to speed
- The available energy grows with the square of speed
- A fast run-up makes the pole stiffer
- Horizontal speed is kept intact above the bar
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The available energy grows with the square of speed
KE = ½ m v²: 10% more speed gives 21% more energy, which can be turned into height.