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To mop-clean a floor, a cleaning machine presses a circular mop of radius R vertically down with a total force F and rotates it with a constant angular speed about its axis. If the force F is distributed uniformly over the mop and if coefficient of friction between the mop and the floor is μ , the torque, applied by the machine on the mop is -

1. μ FR/2
2. μ FR/3
3. μ FR/6
4. 3 2 μ FR

Correct answer: 3 2 μ FR

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