A disc is rotatin g aro u n d its cen tre in a horizontal plane at the rate of 60 rotation/ minute. A coin (1A^(st)) is placed at a distance of 18 cm and 2^(nd) similar coin 20 cm from its centre.The co-efficient of static friction between the disc and the coins is 0.2. Which coin will be thrown away from the disc ? Which coin will keep rotating with the disc ?

A disc is rotatin g aro u n d its cen tre in a horizontal plane at the

1.	A disc is rotatin g aro u n d its cen tre in a horizontal plane at the rate of 60 rotation/ minute. A coin (1A^(st)) is placed at a distance of 18 cm and 2^(nd) similar coin 20 cm from its centre.The co-efficient of static friction between the disc and the coins is 0.2. Which coin will be thrown away from the disc ? Which coin will keep rotating with the disc ?
Answer» both COINS THROWN away 2ndcoin KEEP rotating1st coin thrown away both coins keep rotating 1st coin keep rotating 2nd coin thrownaway Solution :Supposemass of each coin m for the circularmotioncentrifugalforce`le ` maximumstaticfriction. `(mv^(2))/(r ) le f _(s)` Timerequiredfor 60rotationis 60second Timerequiredfor 1rotationis `T = (60)/(60)=1` Now linearvelocity`v=(2pi r)/( T )` and`f_(s(max))= mu_(s ) N = mu_(s ) MG` fromequation(1) `(m )/(T) xx (2pi r)/(T ) le mu_(s ) mg` `le((0.2).(10).(1)^(2))/(4xx 10)` `le0.05 m` `r le m` boththe coin from the 18 cm and 20 cmdistancefrom the centreare thrownaway .