First slide
Law of conservation of angular momentum
Question

A circular platform is free to rotate in a horizontal plane about a vertical axis passing through its centre. A tortoise is sitting at the edge of the platform. Now the platform is given an angular velocity ω0 When the tortoise moves along a chord of platform with a constant velocity (with respect to the platform), the angular velocity of the platform ω(t) will vary with time t as

Moderate
Solution

 Since no external torque is acting on the system , its angular momentum remains conserved  . So Iω = constant .During motion along chord, the distance of tortoise from centre decreases initially and then increases' So, the moment of inertia first decreases and then increases. Hence ω initially increase and then decrease. Also variation in ω is non-linear.

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