College Physics with MasteringPhysics 7th Edition by Jerry Wilson,Anthony Buffa,Bo Lou

Exercise 49

A flat, solid cylindrical grinding wheel with a diameter of 20.2 cm is spinning at 3000 rpm when its power is suddenly turned off. A workman continues to press his tool bit toward the wheel's center at the wheel's circumference so as to continue to grind as the wheel coasts to a stop. If the wheel has a moment of inertia of 4.73 kg · m 2 , (a) determine the necessary torque that must be exerted by the workman to bring it to rest in 10.5 s. Ignore any friction at the axle. (b) If the coefficient of kinetic friction between the tool bit and the wheel surface is 0.85, how hard must the workman push on the bit