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aw2693
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Homework Statement
A grindstone is used to sharpen knives and consists of a stone cylinder and a central axle There are bearings between the axle and the frame to reduce any friction.
This grindstone has a mass of 60 kg, a diameter of 0.600 m and has a moment of Inertia (I) of 4.50 kg.m2 . There is a constant friction torque of 5N.m at the bearings.
(a) You press a knife down on the rim of the grindstone with a normal force of 50N. The coefficient of friction between the knife and the stone is 0.60. How much force must be applied to the outer edge of the grindstone to maintain a constant angular velocity of 120 revolutions per minutes.[14]
(b) How much time does it take for the grindstone to go from 120 revolutions per minute to rest if it is acted up by the bearings friction alone? [6]
Homework Equations
I=1/2mR^2
F=ma
The Attempt at a Solution
Hi, could someone please tell me how to do section a). I have never done physics before and have no real idea where to start. My lecturer assumes everyone has a good standing in the subject but I have not. This is preparation for my exam coming up so any help would be highly appreciated.