A one kg stone attached to the end of a 60 cm chain is revolving at the rate of 3 revolutions/second. If after 30 second, it is making only one revolution per second, find the mean torque

The torque τis given byτ= change in momentum  time taken Here,  L1=mr2ω1=mr2×2πv1and L2=mr2ω2=mr2×2πv2so, change in momentum=mr2×2πv1−v2∴ τ=mr2×2πv1−v2t      =1(0⋅6)2×2π(3−1)30       =0⋅15N−m.