A horizontal turntable is a disk free to rotate frictionlessly around its centra

Question

A horizontal turntable is a disk free to rotate frictionlessly around its central axis. Initially it is at rest, and a coin is resting on it at position A (a distance rA from the axis), as shown here. Then a constant torque, t, is applied to the turn- table (around its central axis) for a certain time interval, Dt. At end of Dt, the torque ceases. At that very same moment (the end of Dt), the coin slips and begins to slide across the surface of the turntable. It stops slipping at position B (a radial distance d from A), as shown, because it encounters an obstruction in the turntable surface. The mass of the coin is m. The moment of inertia of the turntable (without the coin), around its central axis, is I. After the coin has arrived at position B (after it has stopped slipping), the friction force on the coin is half the maximum possible. Find the steady force magnitude exerted by the obstruction on the coin after it has arrived at position B (after it has stopped slipping). You may consider these values as known: rA, t, Dt, d, m, I, g.

Explanation / Answer

let coeff be k km = mv/((r+d)^2) hence k = v/((r+d)^2)

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