A circular display platform can rotate about a vertical axle through its centre. Three ropes apply horizontal forces to the platform. The table gives the force applied by each rope, the distance from the axle to the line of action of the force, and the direction of its moment.
| rope | force | distance from axle to line of action | direction of moment |
|---|---|---|---|
| P | 60 N | 0.60 m | clockwise |
| Q | 45 N | 40 cm | anticlockwise |
| R | FFF | 0.30 m | anticlockwise |
The platform is in rotational equilibrium.
Calculate the force F F\,F applied by rope R.
Rope R continues to apply the force calculated in part (a), but its line of action is moved to a distance of 0.20 m from the axle. The other forces are unchanged.
Predict the direction in which the platform starts to rotate. Explain your answer.
102 exam-style questions on Edexcel GCSE Physics 9.2 Moments, covering 9.2.1 Rotational effects of forces and moments, 9.2.2 The principle of moments, and 9.2.3 Levers and gears. Each one has a worked solution and a mark scheme showing where the marks go.