A horizontal circular platform of radius 0.5 m and mass axis. Two massless spring toy-guns, each carrying a steel ball of mass 0.05 kg are attached to the platform at a distance 0.25m 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 horizontal speed of `9ms^(-1)` with respect to the ground. The rotational speed of the platform in `rad s^(-1)` after the balls leace the platform is

Answer

D

Explanation

Since net torque about centre of rotation is zero, so we can apply conservation of angular of the system about center of disc.
`L_(i) = L_(f)`
`0 = Iomega + 2mv (r //2),` comparing magnitudes.
`therefore ((0.45 xx 0.5 xx 0.5))/2 omega = 0.05 xx 9 xx (0.5)/2 xx 2, therefore omega =4`