A uniform horizontal circular platform of mass `200 kg` is rotating at 10 rpm about a vertical axis passing through its center. A boy of mass `50 kg` is standing at its edge. If the boy moves to the center of the platform, the frequency of rotation would become

Options

A. `7.5` rpm
B. `12.5` rpm
C. 15 rpm
D. 20 rpm

Explanation

To solve the problem, we need to apply the principle of conservation of angular momentum. Here’s a step-by-step breakdown of the solution:

### Step 1: Understand the Initial Conditions
We have a circular platform with a mass of 200 kg rotating at 10 revolutions per minute (rpm). A boy with a mass of 50 kg is standing at the edge of the platform.

### Step 2: Calculate Initial Moment of Inertia
The moment of inertia (I) of the system before the boy moves can be calculated as follows:

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