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Kinetic energy and momentum

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Work done and energy transferred are measured in joules (J). The work done on an object can be calculated if the force and distance moved are known.

A change in momentum happens when a force is applied to an object that is moving or is able to move. The total momentum in an explosion or collision stays the same.

Work, force and distance

You should know, and be able to use, the relationship between work done, force applied and distance moved.

Background

Work and energy are measured in the same unit, the joule (J). When an object is moved by a force, energy is transferred and work is done. But work is not a form of energy - it is one of the ways in which energy can be transferred.

The equation

This equation shows the relationship between work done, force applied and distance moved:

work done (joule, J) = force (newton, N) × distance (metre, m)

The distance involved is the distance moved in the direction of the applied force.

Question

A force of 10N is applied to a box to move it 2m along the floor. What is the work done on the box?

The work done is 10 × 2 = 20J.

Check your understanding of this by having a go at the activity.

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