CAIE IGCSE Physics Extended Multi-Force Moments

Practise applying moments to multi-force beams, rods, bridges and body models, choosing directions and distances from diagrams.

Exam points

combine several clockwise and anticlockwise moments about a chosen pivot
calculate support reactions or applied forces on bridges, rods and loaded bodies
interpret upward and downward forces to predict the direction of rotation

[Maximum number: 3]

A rock climber, of total mass 62 kg , holds herself in horizontal equilibrium against a vertical cliff. She pulls on a rope that is fixed at the top of the cliff and presses her feet against the cliff.

Fig. 3.1 shows her position.

Fig. 3.1 (not to scale)

The climber's centre of mass is 0.90 m from the cliff.

The line of the rope meets the horizontal line through her centre of mass at a distance of 1.2 m from the cliff, as shown in Fig. 3.1. The rope is at an angle of $60^{\circ}$ to the horizontal.

Determine the tension in the rope.
tension = [3]
[Total: 8]

540 N

A3

use of any moment

C1

$T \times 1.2 \sin 60^{\circ}(=560)$ or $(T=) 560 /\left(1.2 \times \sin 60^{\circ}\right)$

C1

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1.5.2.5—Apply the principle of moments to question 1