Linear speed and Friction?

Question

A coin of mass .0050 kg is placed on a disk at a distance of .14m from the center. The coin does not stlip and takes 1.5 s to make a complete revolution.

1. What is the linear speed.
2. The rate of the rotation of the disk increases. The coefficient of static friction is .50. Determine the linear speed of the coin just before it slips.

Answer 1

1. S= 2piR
V=S/t
V= 2 pi R/ t=2 pi R/ 1.5=0.59 m/s
2. f=ma
a=V^2/R
f= u mg
V=sqrt(u mg R/m)
V= sqrt(u g R)
V= sqrt( .5 x 9.81 x .14)=0.83 m/s

Answer 2

just use some little formulas of rotational motion