JEE Main201910 Jan 2019Morning ShiftPhysicsRotational MotionActual
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:
Options
- A2 μ F R / 3
- Bμ F R / 3
- Cμ F R / 6
- Dμ F R / 2
Correct answer
A. 2 μ F R / 3
Step-by-step solution
Net torque = ∑ T o r q u e o n r i n g ∫ d τ = ∫ 0 R μ × F π R 2 × 2 π x d x x τ = 2 μ 3 F R