Physics
posted by Chloe on .
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 36.4° and then moves down the incline with constant speed when the angle is reduced to 29.9°. From these data, determine the coefficients of static and kinetic friction for this experiment.
Any help would be great, thanks for your time!

When there is no acceleration, the friction force (M g cosA *mu) equals the component of the weight in the direction down and parallel to the incline (M g sin A).
Therefore mu = sin A/cos A = tan A
Apply that equation both at the maximum ramp angle before slipping (in which case mu is the static friction coefficient) and the ramp angle that results in constant velocity (in which case mu is the kinetic friction coefficient). 
So static: 0.73 and kinetic: 0.57, thanks!

Static friction is the friction acting on a body when the body is not in motion, but when a force is acting on it. Static friction is the same as the force being applied (because the body isn't moving). Static friction acts because the body tends to move when a force is applied on it.
Limiting friction is the friction on a body just before it starts moving. Generally, limiting friction is highest.