You remember the relationship between the change in Kinetic Energy of an object and the Work done by forces on it, right?
A chunk of ice of mass m = 2 kg sits motionless on a frictionless frozen pond. Then a breeze starts to push the ice cube with a constant force F = 3 N. After the chunk has slid 50 m, how fast is it going?
Well, there are very similar relationships between the angular analogues of these quantities: the change in rotational KE of an object and the Work done on it by torques.
A giant grindstone with radius r = 2 m and moment of inertia I = 700 kg*m^2 is spinning at 10 rpm. Joe slows it down by pressing a wooden brake against the rim of the wheel. How much torque must he exert in order to stop it within 5 revolutions?
How hard must Joe press the brake against the rim of the wheel to cause this to happen?
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