A Levels Physics (9702)•9702/11/O/N/23

Explanation
Torque equilibrium for a uniform bar
Steps:
- Weight W acts at center (L/2 from end A); X at L/4 from A, Y at L from A.
- Vertical force balance: Rx + Ry = W.
- Take torques about X: W acts L/4 to right (clockwise torque W·L/4).
- Ry acts 3L/4 to right (counterclockwise torque Ry·3L/4); set equal: Ry·3L/4 = W·L/4.
- Solve: Ry = W/3, Rx = 2W/3, so Ry/Rx = 1/2.
Why A is correct:
- Torque balance about X directly yields Ry/Rx = 1/2 via the lever arm ratio (distance to W : distance to Ry = 1:3).
Why the others are wrong:
- B: 1/3 ignores torque; confuses with Ry/W.
- C: 3/5 from misplacing center or supports.
- D: 2/5 swaps Rx/Ry ratio.
Final answer: A
Topic: Equilibrium of forces
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