Q.

A ball of mass (m) 0.5 kg is attached to the end of a string having length (L) 0.5 m. The ball is rotated on a horizontal circular path about a vertical axis. The maximum tension that the string can bear is 324 N. The maximum possible value of angular velocity of the ball (in radian/s) is                     [2011]

1 9  
2 18  
3 27  
4 36  

Ans.

(4)

Tsinθ=mRω2                          ...(i)

Tcosθ=mg                               ...(ii)

Dividing (ii) by (i), we get

tanθ=ω2Rg    ω=Rgtanθ

Clearly, ω is maximum when tanθ is maximum, i.e., θ=90°

So, Tsin90°=mRω2

T=mLω2  [Here, R=L]

ω=TmL=3240.5×0.5

         =180.5=36 rad/s