Q.

A solid cylinder of mass 50 kg and radius 0.5 m is free to rotate about the horizontal axis. A massless string is wound round the cylinder with one end attached to it and the other hanging freely. Tension in the string required to produce an angular acceleration of 2 revolutions s-2 is           [2014]

1 25 N  
2 50 N  
3 78.5 N  
4 157 N  

Ans.

(4)

Here, mass of the cylinder, M = 50 kg

Radius of the cylinder, R = 0.5 m

Angular acceleration, α=2rev s-2

=2×2πrad s-2=4πrad s-2

Torque, τ=TR

Moment of inertia of the solid cylinder about its axis, I=12MR2

    Angular acceleration of the cylinder, α=τI=TR12MR2

         T=MRα2=50×0.5×4π2=157N