(c) Given, $MI = 2.5\ kgm^{- 2}$ $W = 40\ rad\ s^{- 1}$ $T = 10\ Nm$ As $T = I\alpha$ $10 = 2.5\alpha$ $\alpha = 4\ rad\ s^{- 2}$ Now, $\omega = \omega_{0} + \alpha t$ $60 = 40 + 4 \times t$ $20 = 4t$ $t = 5\ s$
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Ph.D. in Physics with 19+ years of teaching experience.