A discrevolves with a speed of 33/3rev/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 record ?

A discrevolves with a speed of 33/3rev/min, and has a radius of 15 cm.

1.	A discrevolves with a speed of 33/3rev/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 record ?
Answer» Solution :For the coin to revolve with the DISC, the force of friction should be enough to PROVIDE thenecessary centripital force `i.e (mv^2)/( r) lt= MU MG ` . Now `v = r omega` , where ` omega = (2pi)/( T)` is the angular frequency of the disc.For a given `mu` and `omega` , the condition is `r lt= mu G// omega^2 ` .The condition is satisfied by the nearer coin ( 4 cm from the centre).