A wheel is mounted on a stationary axle which we can assume frictionless. As a r

ID: 2116044 • Letter: A

Question

A wheel is mounted on a stationary axle which we can assume frictionless. As a result, the

wheel can turn freely but cannot translate. The wheel can be described as two concentric rings

of masses 1 kg and 0.5 kg and radii 50 cm and 85 cm. You wrap a string of negligible mass

around the outer ring and pull on it, increasing the angular speed of the wheel from 0 to 8

revolutions per second. Determine: a) How much work is done by you on the pulling; b) If your

hand has moved 3 meters (that is the amount of string that you unwrap in the pulling), how

much is the pulling force?.

I = 1*0.5^2 + 0.5*0.85^2 = 0.61125 kg m^2 ;

Energy = 1/2*I*w^2 = 772.2 J

a) 772.2 J

b)F*3 = 772.2

F =257.4 N

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