When asked the question, "is work done?", you should always consider the definition of work in your response.
When work is done, energy is transferred; energy is the ability to do work.
Key Concepts
Work is done if a body moves in the same direction as a force:
\(W=Fs\)
Work done is measured in Joules (J).
When work is done, energy is transferred from the thing doing the work to the thing it's doing work on (e.g. from a human to a raised apple). The result is that the body will travel faster or move to a higher place.
If the force does not act in the same direction as the motion, the work done will depend on the component of force in the direction of motion:
\(W=Fs\cos \theta\)
In this equation, \(\theta\) refers to the angle between the force and the displacement (will be 0o if parallel)
Consider what happens if \(\theta\) is 90o. If a force and motion are perpendicular (e.g. in circular orbit), no work is done.
Use quizzes to practise application of theory.
START QUIZ!
A box slides along a frictionless surface at constant velocity.
Which statement is correct
work is done when the point of action of a force moves in the direction of the force
A truck pulls a block along a rough surface at constant velocity.
Which of the following statements are true
The point of action of the force pulling the block is moving in the direction of the force. The block doesn't gain energy because it is doing work against friction.
A horizontal force of 10 N pulls a 2 kg block along the floor at a constant velocity of 5ms-1 for 2 s.
The amount of work done is:
Distance travelled = 5 x 2 = 10 m
Motion is horizontal and so is force so Work = 10 x 10
A force of 10 N acts towards the centre of the circle as a 2 kg mass travels with constant speed around a circle of circumference 1 m.
The amount of work done is:
Force is perpendicular to motion, no work done.
How much of Work done have you understood?
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