Discussion Forum

1)

A horizontal circular platform of radius 0.5m  and mass 0.45kg is free to rotate about its axis. Two, assless spring toy-guns, each carrying a steel ball of mass 0.05kg are attached to the platform at a distance 0.25 m from the centre on its either sides along its diameter (see figure) . Each gun simultaneously fires the balls horizontally and perpendicular to the diameter in opposite directions. After leaving the platform, the balls have a horizontal speed of  9 ms^-1 with respect to the ground. The rotational speed of the   platform in rad s^-1  after the balls leave  the platform is 

Answer:

Option A

Explanation:

Applying conservation of angular momentum.

 

$2mvr-\frac{MR^{2}}{2}\omega=0$

$\omega=\frac{4mvr}{MR^{2}}$

 Substituting the values , we get

$\omega=\frac{(4)(5\times 10^{-2})(9)(\frac{1}{4})}{45\times10^{-2}\times\frac{1}{4}}=4 rad/s$