Rotational motion, find the frictional force.

[Enginseer]

Homework Statement

A small 350-g collar C can slide on a semicircular rod which is made to rotate about the vertical AB at a constant rate of 7.5 rad/s. The coefficients of friction are μs = 0.25 and μk = 0.20.

Homework Equations

Tangent Velocity= Radians*radius
Normal acceleration an= Vt^2/radius

The Attempt at a Solution

 

[Enginseer]

Basically the collar has two forces acting on it. The rotational force and the gravitational force. I used the y-axis for the force components parallel/opposite to the normal force and multiplied the normal force by the kinetic friction which should have given me the frictional force. But the computer program I'm using (Mcgraw hill) says my answer is wrong.