Posted by Bobby C on .
A 32 kg crate is placed on an inclined ramp. When the angle the ramp makes with the horizontal is increased to 23.2° the crate begins to slide downward.
(a) What is the coefficient of static friction between the crate and the ramp?
(b) At what angle does the crate begin to slide if its mass is doubled?
I have no idea how to find part a.
For part B why is it not twice the angle?

Physics 
Damon,
component of the weight down the ramp = m g sin 23.2
component of the weight perpendicular to the ramp = m g cos 23.2 (this is the normal force)
friction force = coef * normal force = weight component down ramp when slip starts
so
mu m g cos 23.2 = m g sin 23.2
solve for mu, the coefficient
Notice that the mass cancels out, it does not matter.