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Dynamics

Newton's second law and F = ma

  • 3 things to know
  • Component 1

Overview

Equation F = ma, defining each symbol and its unit, newton's first law of motion and inertia of a body.

What you need to know

Answer each one before you reveal it.

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Key term

In an investigation of a = F/m with constant total mass, what is plotted and what does the gradient give?

Key term

State Newton's second law in the form used for a body of constant mass.

Key term

State the equation F = ma, defining each symbol and its unit.

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    State Newton's second law in the form used for a body of constant mass.

    Model answer

    The resultant force on a body of constant mass is equal to its mass multiplied by its acceleration, and the acceleration is in the direction of that resultant force.

  2. 2

    State the equation F = ma, defining each symbol and its unit.

    Model answer

    In F = ma, F is the resultant force in N, m is the mass in kg and a is the acceleration in m s⁻².

  3. 3

    Why must the F in F = ma be the resultant force and not just any one of the forces acting?

    Model answer

    Only the resultant determines how the motion changes, since forces that balance produce no acceleration at all.

  4. 4

    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.

  5. 5

    What is meant by the inertia of a body, and which quantity measures it?

    Model answer

    Inertia is a body's resistance to any change in its state of motion, and mass is the measure of it.

  6. 6

    A resultant force of 3600 N acts on a car of mass 1200 kg. Calculate the acceleration.

    Model answer

    The acceleration is 3600 ÷ 1200 = 3.0 m s⁻² in the direction of the force. Multiplying 1200 kg by 3.0 m s⁻² returns 3600 N.

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