OCR A-Level Physics B H557
Planning
Implementing
Analysis
Evaluation
Practical Skills
Use of Apparatus and Techniques
Fundamental Data Analysis
Imaging and Signalling
Sensing
Mechanical Properties of Materials
Waves and Quantum Behaviour
Space, Time and Motion
Creating Models
Out Into Space
Our Place in the Universe
Matter: Very Simple
Matter: Hot or Cold
Electromagnetism
Charge and Field
Probing Deep Into Matter
Ionising Radiation and Risk
Space, Time and Motion
Newton's laws of motion
- 3 things to know
- Components 01, 02 and 03
Overview
Recall questions on Newton's first, second and third laws, F = ma from the momentum form, resultant force, car and football calculations, why third law pairs never cancel, the partner of a book's weight, a passenger thrown forwards, the newton, mass as inertia, rocket propulsion, and the floor force in an accelerating lift.
What you need to know
Answer each one before you reveal it.
Show how F = ma follows from the momentum form of Newton's second law when the mass is constant.
A resultant force of 3.0 kN acts on a car of mass 1500 kg. What is its acceleration?
Questions from this subtopic
Each one with the model answer underneath.
- 1
State Newton's first law of motion.
Model answer
A body remains at rest or continues to move at constant velocity in a straight line unless a resultant force acts on it.
- 2
State Newton's second law of motion in terms of momentum.
Model answer
The resultant force on a body equals the rate of change of its momentum, F = Δ(mv)/Δt.
- 3
Show how F = ma follows from the momentum form of Newton's second law when the mass is constant.
Model answer
With m constant, Δ(mv)/Δt becomes m Δv/Δt, and Δv/Δt is the acceleration, so F = ma.
- 4
State Newton's third law of motion.
Model answer
If body A exerts a force on body B, then B exerts a force on A that is equal in size, opposite in direction and of the same kind.
- 5
What is meant by the resultant force acting on a body?
Model answer
It is the single force equal to the vector sum of all the individual forces acting on that body.
- 6
A resultant force of 3.0 kN acts on a car of mass 1500 kg. What is its acceleration?
Model answer
a = F/m = 3000/1500 = 2.0 m s⁻².
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