CCEA A Level Physics
CCEA A Level Physics 1.6 Newton's Laws of Motion and 1.7 Linear Momentum and Impulse Exam Questions
Free CCEA A Level Physics revision for 1.6 Newton's Laws of Motion and 1.7 Linear Momentum and Impulse: what you need to know, common mistakes and exam-style questions with answers. Covers newton's three laws, F = ma, friction, momentum, conservation of momentum, elastic and inelastic collisions and impulse.
Practise 1.6 Newton's Laws of Motion and 1.7 Linear Momentum and Impulse with past papers
Once you have learnt this topic, find the 1.6 Newton's Laws of Motion and 1.7 Linear Momentum and Impulse questions in real CCEA A Level Physics past papers and mark them with the mark scheme. Doing lots of real questions is the quickest way to learn how examiners ask about each idea.
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About CCEA A Level Physics 1.6 Newton's Laws of Motion and 1.7 Linear Momentum and Impulse
These sections in Unit AS 1: Forces, Energy and Electricity explain why objects move as they do. You need to state and apply Newton's three laws, use F = ma including friction as a force opposing motion, and then move on to linear momentum. Conservation of momentum is applied to one-dimensional collisions and explosions, and you must decide whether a collision is elastic or inelastic by comparing kinetic energy. Impulse links force and time to change in momentum, including the area under a force-time graph. Examiners favour collision calculations, precise statements of laws and explanations of safety features such as crumple zones.
What you need to know
- Newton's first law An object stays at rest or moves with constant velocity unless a resultant external force acts on it.
- Newton's second law Resultant force = mass x acceleration (F = ma) for constant mass. Friction acts opposite to the direction of motion, so the resultant force is driving force minus friction.
- Newton's third law If body A exerts a force on body B, then B exerts an equal and opposite force on A. The pair are the same type of force and act on different bodies.
- Momentum and its conservation Momentum p = mv, a vector with unit kg m s-1. In a closed system with no external force, the total momentum before an interaction equals the total momentum after.
- Elastic and inelastic collisions Momentum is conserved in all collisions. In an elastic collision kinetic energy is also conserved; in an inelastic collision some kinetic energy is transferred to other forms.
- Impulse Impulse = F x t = change in momentum. It equals the area under a force-time graph. Increasing the time of impact reduces the force for the same momentum change.
Common mistakes in 1.6 Newton's Laws of Motion and 1.7 Linear Momentum and Impulse
- Identifying weight and normal reaction as a Newton's third law pair; they act on the same body and are different types of force.
- Ignoring direction in momentum calculations; give one direction a positive sign and objects moving the other way negative momentum.
- Saying kinetic energy is lost in an inelastic collision without saying it is transferred to other forms such as heat and sound.
- Using F = ma with the driving force alone when friction acts; F must be the resultant force.
- Stating conservation of momentum without the condition that no external force acts.
Try three 1.6 Newton's Laws of Motion and 1.7 Linear Momentum and Impulse exam-style questions
1. A trolley of mass 2.0 kg moving at 3.0 m s-1 collides with a stationary trolley of mass 1.0 kg and they stick together. Calculate their common velocity and show the collision is inelastic. (4 marks)
Show the mark scheme answer
Momentum before = 2.0 x 3.0 = 6.0 kg m s-1; v = 6.0/3.0 = 2.0 m s-1; KE before = 1/2 x 2.0 x 3.0^2 = 9.0 J; KE after = 1/2 x 3.0 x 2.0^2 = 6.0 J, so KE is not conserved and the collision is inelastic.
2. A ball of mass 0.15 kg hits a wall at 20 m s-1 and rebounds at 15 m s-1. Contact lasts 0.010 s. Calculate the average force on the ball. (3 marks)
Show the mark scheme answer
Change in momentum = 0.15 x (15 - (-20)) = 5.25 kg m s-1; F = change in momentum / time = 5.25/0.010; = 525 N (about 530 N).
3. State Newton's second law of motion. (1 mark)
Show the mark scheme answer
The resultant force on a body is equal to the rate of change of its momentum (F = ma for constant mass), in the direction of the resultant force.
1.6 Newton's Laws of Motion and 1.7 Linear Momentum and Impulse FAQs
What does CCEA A Level Physics 1.6 and 1.7 cover?
Newton's three laws, F = ma with friction, linear momentum and its conservation, elastic and inelastic collisions in one dimension, and impulse.
Which unit are these sections examined in?
Both are in Unit AS 1: Forces, Energy and Electricity.
How do I decide if a collision is elastic?
Calculate the total kinetic energy before and after. If it is the same, the collision is elastic; if it falls, it is inelastic. Momentum is conserved in both cases.
