Moments and the Equilibrium of a Rigid Body · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Turns must balance too

Mathematics · Mechanics · ages 17-18
Name ______________________   Date ____________

  1. A 10 N force acts at right angles 2 m from a pivot. What is its moment about the pivot, in N m?

    Answer: ______________

  2. A force acts at right angles to a spanner. Priya says doubling the distance from the nut doubles the moment. Is Priya right?

    Circle one:   True   False

  3. A 6 N force pushes at right angles 0.5 m from a pivot. What is the moment?

    • 3 N m
    • 12 N m
    • 0.5 N m

  4. A 10 N force acts at right angles 2 m from a pivot. What is its moment about the pivot, in N m?

    Answer: ______________

  5. A uniform beam 4 m long weighs 40 N and rests on supports at its ends. A 60 N load sits at its middle. What is each support reaction, in N?

    Answer: ______________

  6. A 6 N force pushes at right angles 2 m from a pivot. What is its moment, in N m?

    Answer: ______________

  7. A force acts at right angles to a spanner. Priya says doubling the distance from the nut doubles the moment. Is Priya right?

    Circle one:   True   False

  8. A 6 N force pushes at right angles 0.5 m from a pivot. What is the moment?

    • 3 N m
    • 6 N m
    • 12 N m
    • 0.5 N m

  9. A uniform 6 m plank weighing 60 N sticks 2 m out past a wall edge. A 40 N child walks out along the overhang. How far past the edge, in m, can the child go before the plank starts to tip?

    Answer: ______________

  10. A uniform 6 m plank weighing 60 N sticks 2 m out past a wall edge. A 40 N child walks out along the overhang. How far past the edge, in m, can the child go before the plank starts to tip?

    Answer: ______________

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Answer key

For grown-ups. Fold this page away before handing over the rest.

Turns must balance too W1-mt_FX5egGL4LI-s1

  1. 20 · Moment is 10 times 2 = 20 N m.
  2. True · Moment is force times distance, so with fixed force it scales directly with distance.
  3. 3 N m · 6 times 0.5 = 3 N m.
  4. 20 · Moment is 10 times 2 = 20 N m.
  5. 50 · Total load is 100 N, split evenly by symmetry, so 50 N at each end.
  6. 12 · Moment is 6 times 2 = 12 N m.
  7. True · Moment is force times distance, so with fixed force it scales directly with distance.
  8. 3 N m · 6 times 0.5 = 3 N m.
  9. 1.5 · The restoring moment is 60 N m, so 40 times d = 60 gives d = 1.5 m.
  10. 1.5 · The plank centre is 1 m inside, giving a restoring moment of 60 N m, so 40 times d = 60 gives d = 1.5 m.
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