Edexcel A-Level Physics 9PH0
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Mechanics
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Mechanics
Free-body diagrams and Newton's first and second laws
- 1 thing to know
- Papers 1 and 3
Overview
Recall questions on what belongs on a free-body diagram, the statements of the first and second laws, the definition of the newton, and applying F = ma.
What you need to know
Answer each one before you reveal it.
Questions from this subtopic
Each one with the model answer underneath.
- 1
What is shown on a free-body force diagram?
Model answer
Only the forces acting on one chosen body, shown as labelled arrows pointing in the directions in which the forces act.
- 2
Why are the forces that the chosen body exerts on other objects left out of its free-body diagram?
Model answer
Those forces act on other bodies, so they cannot contribute to the resultant force on the body being considered.
- 3
What should the length of each arrow on a free-body force diagram indicate?
Model answer
The relative magnitude of that force.
- 4
Which forces act on a book resting on a horizontal table?
Model answer
Its weight acting vertically downwards and the normal contact force from the table acting vertically upwards, which are equal in magnitude.
- 5
Which forces act on a car moving at constant velocity along a level road?
Model answer
Weight downwards, normal contact force upwards, the driving force forwards and the resistive forces backwards, with each pair equal in magnitude.
- 6
What does Newton's first law of motion state?
Model answer
A body stays at rest or continues to move at constant velocity in a straight line unless a resultant external force acts on it.
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