Edexcel A-Level Physics 9PH0
Working as a Physicist
Mechanics
Electric Circuits
Materials
Waves and Particle Nature of Light
Further Mechanics
Electric and Magnetic Fields
Nuclear and Particle Physics
Thermodynamics
Space
Nuclear Radiation
Gravitational Fields
Oscillations
Mechanics
Work done by a force
- 1 thing to know
- Papers 1 and 3
Overview
Recall questions on the definition of work and the joule, the cosine term when a force acts at an angle, and what negative work means.
What you need to know
Answer each one before you reveal it.
Questions from this subtopic
Each one with the model answer underneath.
- 1
How is the work done by a force defined, and what is its equation?
Model answer
Work done is the force multiplied by the distance moved in the direction of the force, ΔW = FΔs.
- 2
How is the joule defined?
Model answer
One joule is the work done when a force of 1 N moves its point of application 1 m in the direction of the force.
- 3
How is the work done calculated when the force acts at an angle θ to the direction of motion?
Model answer
The work done is ΔW = FΔs cos θ, using the component of the force along the direction of motion.
- 4
Why is no work done by a force that acts at right angles to the motion?
Model answer
Because cos 90° = 0, the force has no component along the displacement and so transfers no energy.
- 5
What is an example of a force that does no work on a moving object?
Model answer
The normal contact force on a box sliding along a horizontal floor does no work, because it acts vertically while the motion is horizontal.
- 6
A suitcase is pulled 15 m along level ground by a force of 60 N acting at 25° above the horizontal. How much work does that force do?
Model answer
The work done is 60 × 15 × cos 25° = 816 J.
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