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JEE Advanced2014PhysicsRotational MotionActual

A horizontal circular platform of radius 0.5 m and mass 0.45 kg is free to rotate about its axis. Two massless spring toy-guns, each carrying a steel ball of mass 0.05 kg are attached to the platform at a distance 0.25 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 p

Correct answer

4

Step-by-step solution

Since net torque about centre of rotation is zero, so we can apply conservation of angular momentum of the system about center of disc L i = L f 0 = I ω + 2 m v r 2 ; comparing magnitude ∴ 0.45 × 0.5 × 0.5 2 ω = 0.05 × 9 × 0.5 2 × 2 ∴ ω = 4

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