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Chapter 5 Practice Paper: Turning Effects of Forces — question paper

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QQ/S3CPH/CH5

Secondary 3 · Combined Science (Physics) (G2 / G3)

Chapter 5 Practice Paper

Turning Effects of Forces

Duration: 40 minutes
Total: 30 marks
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READ THESE INSTRUCTIONS FIRST

  • Answer all questions.
  • Section A: choose the one correct answer for each multiple-choice question.
  • Section B: answer in the spaces provided; show all necessary working.
  • Give numerical answers to 3 significant figures where appropriate, with units.
  • The acceleration of free fall near the Earth is 10 m/s².
  • The use of a calculator is permitted.

Original practice material written for the MOE Combined Science (Physics) syllabus. It is not an official MOE or school examination paper. Chapter 5 (moment = force × perpendicular distance, principle of moments, centre of gravity of uniform rules).

For Examiner’s Use
Section A/ 10
Section B/ 20
Total/ 30

Section A: Multiple-choice questions[10 marks]

Choose the one correct answer for each question.

  1. 1

    A moment is the

    1. Aforce on a surface per unit area
    2. Bturning effect of a force about a pivot
    3. Cenergy stored in a stretched spring
    4. Dpush needed to start an object moving
    ( )
  2. 2

    A 25 N force acts 0.40 m from a pivot, its line of action perpendicular to the lever arm. Calculate the moment about the pivot.

    1. A0.016 N m
    2. B10 N m
    3. C62.5 N m
    4. D100 N m
    ( )
  3. 3

    A push of 15 N is applied along the lever, straight at the pivot. The moment about the pivot is

    1. Azero
    2. B15 N m
    3. Cdepends on the lever length
    4. Dmaximum
    ( )
  4. 4

    A uniform metre rule balances on a knife-edge at the 50 cm mark. This shows the rule’s centre of gravity is at

    1. Athe 0 cm mark
    2. Bthe 25 cm mark
    3. Cthe 50 cm mark
    4. Dthe 100 cm mark
    ( )
  5. 5

    A load hangs 0.20 m from a pivot, producing a moment. To halve the moment with the same load, hang it

    1. A0.10 m from the pivot
    2. B0.40 m from the pivot
    3. Ctwice as heavy
    4. Dat the pivot’s level
    ( )

Section B: Structured questions[20 marks]

Answer all questions in the spaces provided. Show all necessary working.

  1. 1

    A uniform metre rule is pivoted at its centre (the 50 cm mark). A 3.0 N weight hangs from the 20 cm mark.

    1. (a)

      Calculate the anticlockwise moment of the 3.0 N weight about the pivot.

      moment =N m[2]
    2. (b)

      Calculate the distance from the pivot at which a 4.5 N weight must hang on the right to balance the rule.

      distance =m[2]
    3. (c)

      State the reading on the rule at which the 4.5 N weight hangs.

      [1]
    4. (d)

      State why the rule’s own weight does not appear in the balance.

      [1]
  2. 2

    A mechanic uses a 45 cm spanner. A force of 60 N is applied at the free end, perpendicular to the spanner, to turn a bolt (the pivot).

    1. (a)

      Calculate the moment about the bolt.

      moment =N m[2]
    2. (b)

      The bolt needs a moment of 40 N m to loosen. Calculate the smallest force the mechanic must apply at the end of the spanner.

      force =N[2]
    3. (c)

      The mechanic switches to a 60 cm spanner. Calculate the force now needed, and state the advantage of the longer spanner.

      [3]
  3. 3

    A non-uniform plank of weight 96 N balances on a pivot at the 62 cm mark with no weights attached. A 20 N weight is then hung at the 22 cm mark.

    1. (a)

      State the position of the plank’s centre of gravity, with a reason.

      [2]
    2. (b)

      Calculate the moment of the 20 N weight about the pivot, and state its direction of turning.

      moment =N m[2]
    3. (c)

      Calculate the weight that must hang at the 92 cm mark to restore balance.

      [3]

— End of paper —