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Linear Momentum and Impulse

  • 7 subtopics
  • 21 things to know
  • Unit AS 1

What Linear Momentum and Impulse covers

Linear Momentum and Impulse is examined in Unit AS 1, Forces, Energy and Electricity, and drawn on again in Unit AS 3, Practical Techniques and Data Analysis. It covers momentum and its calculation, conservation of linear momentum, collisions in one dimension, elastic and inelastic collisions, impulse and the impulse–momentum equation, Impacts and reducing the force of a collision and newton's second law in terms of momentum.

Where it is assessed

Unit AS 1

Forces, Energy and Electricity, and again in Unit AS 3, Practical Techniques and Data Analysis.

Check the CCEA specification ↗

The 7 subtopics

Each one has its own page.

What you need to know

Answer each one before you reveal it.

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Key term

State the equation for momentum, defining each symbol and its unit.

Key term

State the unit of momentum and show that it is equivalent to the newton second.

Key term

Explain why a direction must always be given when quoting a momentum.

Key term

Explain what conservation of momentum requires of the fragments of an object that explodes from rest.

Key term

Describe how the conservation of linear momentum is verified in a collision using trolleys and light gates.

Key term

Explain why the total momentum measured after a trolley collision is often slightly less than the total measured before.

Key term

State the momentum equation for a one-dimensional collision between two bodies, defining each symbol.

Numbers

A 2.0 kg trolley travelling at 5.0 m s⁻¹ collides with a stationary 3.0 kg trolley and the two stick together. Calculate their common velocity.

Key term

Define an inelastic collision.

Key term

State which quantity is conserved in every collision, whatever its type.

Key term

Explain why kinetic energy can be lost in a collision while momentum is still conserved.

Key term

State the impulse–momentum equation, defining each symbol and its unit.

Key term

Explain why the change in momentum in a crash is fixed while the force on the occupants is not.

Key term

Explain how the crumple zone of a car protects the occupants.

Key term

State the momentum form of Newton's second law as an equation, defining each symbol and its unit.

Key term

Give an example of a situation in which the momentum form applies but F = ma does not.

Numbers

A rocket engine ejects 20 kg of exhaust gas each second at 500 m s⁻¹. Calculate the thrust produced.

Key term

State the unit of impulse and show that it is the same as the unit of momentum.

Process

Outline the steps used to solve a one-dimensional collision problem.

Key term

State in words what the impulse–momentum equation says.

Key term

State the relationship that explains why lengthening the time of an impact reduces the force on the bodies involved.

Take Linear Momentum and Impulse further

The same content, four other ways.

Questions from this topic

Each one with the model answer underneath.

  1. 1

    Define momentum.

    Model answer

    Momentum is the product of the mass of a body and its velocity, and it is a vector quantity acting in the direction of the velocity.

  2. 2

    State the equation for momentum, defining each symbol and its unit.

    Model answer

    Momentum is p = mv, where p is the momentum in kilogram metres per second (kg m s⁻¹), m is the mass in kilograms and v is the velocity in metres per second.

  3. 3

    State the unit of momentum and show that it is equivalent to the newton second.

    Model answer

    The unit is kg m s⁻¹; since 1 N = 1 kg m s⁻², multiplying by a second gives 1 N s = 1 kg m s⁻¹, so the two units are the same.

  4. 4

    Explain why a direction must always be given when quoting a momentum.

    Model answer

    Momentum is a vector, so two bodies of equal mass and speed travelling in opposite directions have momenta that cancel rather than add, and only the stated direction distinguishes them.

  5. 5

    Explain the sign convention used when handling momentum along a straight line.

    Model answer

    One direction along the line is chosen as positive at the start, and any momentum directed the other way is entered into the calculation as a negative number.

  6. 6

    A car of mass 1200 kg travels due east at 15 m s⁻¹. Calculate its momentum.

    Model answer

    Using p = mv, p = 1200 × 15 = 1.8 × 10⁴ kg m s⁻¹ directed due east; checking back, 18 000 ÷ 1200 = 15 m s⁻¹, which is the velocity given.

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Linear Momentum and Impulse revision questions

What does Linear Momentum and Impulse cover in CCEA A-Level Physics?
7 subtopics: momentum and its calculation, conservation of linear momentum, collisions in one dimension, elastic and inelastic collisions, impulse and the impulse–momentum equation, impacts and reducing the force of a collision and newton's second law in terms of momentum. Each one has its own page with questions and model answers.
How is Linear Momentum and Impulse organised?
By the CCEA 1210 specification, subtopic by subtopic, so it matches the order you are taught it in.

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