The pulley shown in figure has a moment of inertia I about its axis and its radius is r. Calculate the magnitude of the acceleration of the two blocks. Assume that the string is light and does not slip on the pulley.
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Solution
Suppose the tension in the left string is T1 and that in the right string in T2. Suppose the block of mass m1 goes, down with an acceleration α and the other block moves up with the same acceleration. This is also the tanqential acceleratlon of the rim of the wheel as the string does not slip over the rim. The angular acceleration of the wheel is, therefore, α=a/r. The equations .of motion for the mass m1, the mass m2 and the pulley are as follows : m1g−T1=m1a .......... (i) T2−m2g=m2a .......... (ii) T1r−T2r=lα=lα/r .......... (iii) Putting T1andT2 from (i), and (ii) into (iii), [(m1g−a)−m2(g+a)]rIar Which gives a =(m1−m2)gr3I+(m1+m2)r2