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Young University Physics 12e: Mastering Physics Problem 10.53

A 70.0-kg grindstone is a solid disk 0.540 m in diameter. You press an ax down on the rim with a normal force of 150 N. The coefficient of kinetic friction between the blade and the stone is 0.60, and there is a constant friction torque of 6.50 Nm between the axle of the stone and its bearings.

Part A

How much force must be applied tangentially at the end of a crank handle 0.500 m long to bring the stone from rest to 120 rev/min in 9.00 s ?

Part B

After the grindstone attains an angular speed of 120 rev/min, what tangential force at the end of the handle is needed to maintain a constant angular speed of 120 rev/min?

Part C

How much time does it take the grindstone to come from 120 rev/min to rest if it is acted on by the axle friction alone?

2. Relevant equations

Torque = Radius(R) x Force(F) or Moment of Inertia(I) x Angular Acceleration(alpha)

3. The attempt at a solution

Not even sure how to do part A

Do I need to include the negative torque done by the ax along with the friction on the bearings in my calculation for part A?

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# Homework Help: Torque and Forces of grindstone

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