Question

Please answer the question given below

Answer 1

Since the kinetic energies of both are same, the change in kinetic energy for both coming to rest are also same.

$\displaystyle\longrightarrow\sf{KE_1=KE_2}$

$\displaystyle\Longrightarrow\sf{\Delta KE_1=\Delta KE_2}$

By work - energy theorem,

$\displaystyle\longrightarrow\sf{\tau_1\theta_1=\tau_2\theta_2}$

Because work - energy theorem for a rotating body states that,

$\displaystyle\longrightarrow\sf{\Delta KE=\tau\theta}$

But here, $\displaystyle\sf{\tau_1=\tau_2=\tau.}$ Then,

$\displaystyle\longrightarrow\sf{\tau\theta_1=\tau\theta_2}$

$\displaystyle\longrightarrow\sf{\theta_1=\theta_2}$

Therefore, the disc also completes n revolutions before coming to rest.