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Moments and equilibriumEdexcel International A Level Physics: Flashcards

What these 13 flashcards ask

  • Define the moment of a force about a point.
  • What is the unit of moment?
  • A force F acts at angle θ to a rod of length L pivoted at one end. What is its moment about the pivot?
  • What is meant by the centre of gravity of an object?
  • Where is the centre of gravity of a uniform rod?
  • State the principle of moments.
  • What two conditions must be met for a body to be in equilibrium?
  • Why is it useful to take moments about a hinge or pivot?
  • A 40 N force acts at right angles at the end of a 0.25 m spanner. What is the moment?
  • Why does a longer spanner make a nut easier to turn?
  • A uniform plank of weight 200 N and length 4.0 m rests on supports at its ends. What force does each support exert with no load?
  • What is the line of action of a force?
  • A body is in equilibrium. What can be said about the total upward and total downward forces?

Exam questions on Moments and equilibrium

  1. A mechanic uses a spanner with a handle 0.25 m long to tighten a nut. The force is applied at the end of the handle, and the axis of rotation is the centre of the nut.
    Explain why a longer spanner makes it easier to turn the nut.2 marks
  2. A uniform plank of length 4.0 m and weight 200 N rests horizontally on two supports, A at its left end and B at its right end. A child of weight 600 N stands on the plank 1.0 m from A.
    State what is meant by the centre of gravity of an object, and explain why the weight of the plank can be taken to act at a point 2.0 m from A.2 marks
  3. A uniform metre rule of weight 1.0 N is pivoted on a knife edge at the 30.0 cm mark. A 2.0 N weight is hung from the 5.0 cm mark and a weight W is hung from the 90.0 cm mark. The rule balances horizontally.
    Calculate the weight W.3 marks
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Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).