A Levels Physics (9702)•9702/11/M/J/21

Explanation
Net torque about pivot P is 6 N m clockwise
Steps:
- Calculate torque from 16 N force at 0.3 m from P: 16 × 0.3 = 4.8 N m clockwise.
- Calculate torque from 20 N force at 0.9 m from P: 20 × 0.9 = 18 N m counterclockwise.
- Net torque without F: 4.8 - 18 = -13.2 N m (13.2 N m counterclockwise).
- For net +6 N m clockwise, torque from F at 1.2 m: 1.2F = 13.2 + 6 = 19.2; F = 19.2 / 1.2 = 16 N.
Why C is correct:
- 16 N produces exactly 19.2 N m clockwise torque, balancing to net 6 N m clockwise per torque equation ∑M_P = 6.
Why the others are wrong:
- A: 9.2 N gives 11.0 N m torque, net -2.2 N m (counterclockwise).
- B: 11 N gives 13.2 N m torque, net 0 N m.
- D: 24 N gives 28.8 N m torque, net 15.6 N m (excess clockwise).
Final answer: C
Topic: Turning effects of forces
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