WACE Physics Practice Questions
The 64 practice questions inside the WACE Physics Mastery Pack, grouped by area of study. Every question comes with a full worked solution.
- Gravity and relativity
- Multiple choice × 24
- Written response × 8
- Electromagnetism and modern physics
- Multiple choice × 24
- Written response × 8
A horizontal 4.00 m beam is hinged at its left end. Its weight of 160 N acts at its midpoint, and a 240 N load acts 3.50 m from the hinge. A cable attached to the right end pulls upward and left at 30.0° above the beam. The system is stationary. (a) Calculate cable tension. (3 marks) (b) Determine the horizontal and vertical hinge-force components. (3 marks) (c) Explain why the hinge force can be eliminated from one equation but not from the whole solution. (2 marks)
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Answer: Worked solution
(a) Taking moments about the hinge removes its zero-lever-arm force. Anticlockwise moment is (T sin 30.0°)(4.00); clockwise moment is 160(2.00) + 240(3.50) = 1160 N m. Therefore T = 580 N. The cable's full tension is not perpendicular to the beam, so using 4 T would give the wrong result.
(b) The cable's upward component is 290 N and leftward component is T cos 30.0° = 502 N. Horizontal force balance requires hinge force 502 N right. Vertical balance gives Hy + 290 − 160 − 240 = 0, so Hy = 110 N upward. These components describe the force on the beam, not the opposite force that the beam exerts on the wall.
(c) The hinge force has no moment about the hinge because its line of action passes through the chosen pivot. It still contributes to translational equilibrium, so both component force balances are required. Zero net torque alone would permit an unbalanced translating beam.
Marking: (a) Correct moment arms and equation: 1; resolving the cable force: 1; tension 580 N: 1. (b) Horizontal magnitude 502 N: 1; rightward direction: 1; vertical 110 N upward: 1. (c) Zero moment about the hinge: 1; continued role in force balance: 1.
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