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Further Mechanics

Impulse and force-time graphs

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  • Papers 1 and 3

Overview

Recall questions on impulse and why it shares momentum's unit, Newton's second law in momentum form, the area under a force-time graph, and why a crumple zone reduces force.

What you need to know

Answer each one before you reveal it.

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Numbers

What is the unit of momentum and impulse, how is Newton's second law written using momentum, and what does a force-time area give?

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    What is the linear momentum of a body, and what kind of quantity is it?

    Model answer

    Momentum is the product of a body's mass and its velocity, p = mv, and it is a vector quantity acting in the direction of the velocity.

  2. 2

    State the SI unit of momentum and the equivalent unit used for impulse:

    Model answer

    Momentum is measured in kg m s⁻¹, which is identical to the newton second, N s.

  3. 3

    How is Newton's second law stated in terms of momentum?

    Model answer

    The resultant force acting on a body equals its rate of change of momentum, F = Δp/Δt.

  4. 4

    What is meant by the impulse of a force?

    Model answer

    Impulse is the product of a force and the time for which it acts, FΔt, and it equals the change of momentum it produces.

  5. 5

    Why do impulse and momentum share the same unit?

    Model answer

    Impulse is equal to the change of momentum, so N s and kg m s⁻¹ must reduce to the same combination of base units.

  6. 6

    What physical quantity is represented by the area under a force–time graph?

    Model answer

    The area represents the impulse delivered, which is equal to the change of momentum of the body.

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