Calculating Coefficients of Friction with an Inclined Eraser

[piercegirl]

Homework Statement

In order to determine the coefficients of friction between rubber and various surfaces, a student uses a rubber eraser and an incline. In one experiment, the eraser begins to slip down the incline when the angle of inclination is 35.2° and then moves down the incline with constant speed when the angle is reduced to 30.8°. From these data, determine the coefficients of static and kinetic friction for this experiment.
FIND: Static and Friction

Homework Equations

f=mu(N)

The Attempt at a Solution

N=mgcos(theta)

 

[frogjg2003]

What seems to be the problem? You haven't really shown any attempt at solving the problem.

 

[piercegirl]

Well i guess I am just confused on the following: I know that static friction is bigger and requires more force than that of friction force. The angles seem to indicate that the Static is 30.8 and friction is 35.2 is that right?

 

[frogjg2003]

In one experiment, the eraser begins to slip down the incline when the angle of inclination is 35.2° and then moves down the incline with constant speed when the angle is reduced to 30.8°.

When does static friction apply? When does kinetic friction apply?

Draw a force diagram. Is the motion in equilibrium?