Discussion Forum



1)

A disc has mass 'M' and radius  'R'. How much tangential force should be applied to the rim of the disc, so as to rotate with angular velocity '$\omega$ ' in time 't'?


A) $\frac{MR\omega}{4t}$

B) $\frac{MR\omega}{2t}$

C) $\frac{MR\omega}{t}$

D) $MR\omega t$

Answer:

Option B

Explanation:

 Given, mass of disc= M

 Radius of disc= R

 we know that,

   $\tau= l\alpha$

 But , $\tau= F\times R$

 $\therefore$   $l= \frac{MR^{2}}{2}$

 and   $\alpha= \frac{\omega}{t}$

 therefore  , F x R= $\frac{MR^{2}}{2}\times\frac{\omega}{t}$

 F= $\frac{MR\omega}{2t}$