Question

A disc revolves with a speed 33\(\frac {1}{3}\) of rev/min, and has a radius of 15 cm. Two coins are placed at 4 cm and 14 cm away from the centre of the record. If the co-efficient of friction between the coins and the record is 0.15, which of the coins will revolve with the

Answer 1

If the coin is to revolve with the record then the force of friction must be enough to provide the necessary centripetal force.

i.e. mr ω² ≤ µsmg or r ≤ \(\frac{μsg}{ω^2}\)

Here, ω = 33 \(\frac {1}{3}\)rpm

The coin placed within the radial distance of 0.12 m will revolve with the record. Hence coin at 4 cm will revolve with the record.