A 235 kg merry-go-round in the shape of auniform, solid, horizontal disk of radi

Question

A 235 kg merry-go-round in the shape of auniform, solid, horizontal disk of radius 1.50 m is set in motionby wrapping a rope about the rim of the disk and pulling on therope. What constant force would have to be exerted on the rope tobring the merry-go-round from rest to an angular speed of0.800 rev/s in 2.00 s?
1 N


A potter's wheel having a radius 0.49 mand a moment of inertia 12.8kg·m2 is rotating freely at 51 rev/min. The potter can stop the wheel in7.5 s by pressing a wet rag against therim and exerting a radially inward force of 70 N. Find the effective coefficient of kineticfriction between the wheel and the wet rag.
1


A meter stick is found to balance at the 49.7 cm mark when placedon a fulcrum. When a 52.0 gram mass isattached at the 9.0 cm mark, the fulcrummust be moved to the 39.2 cm mark for balance. What is the mass ofthe meter stick?
1 g

If the torque required to loosen a nut that is holding a flat tirein place on a car has a magnitude of 40.0N·m, what minimum force must be exerted by themechanic at the end of a 26.0 cm lugwrench to accomplish the task?
1 N

Explanation / Answer

   solution for the second one (potterswheel)   from the theory we have the equation for theangular acceleration as    = (f -i) / t      (i = 0)       = - (i /t)    the torque is given by    = I       = - (I i /t)    the torque is also    = - f r    so the magnitude of the required friction forcewill be    f = I i / r (t)      = (12.8 kg . m2) (51 rev /min) / (0.49 m) (7.5 s) (2 rad / 1 rev) (1 min / 60 s)      = ......... N    now the coefficient of friction will be    k = f / n         = f / (70 N)         =........

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