A 45 kg crate is placed on an inclined ramp. When the angle the ramp makes with the horizontal is increased to 22 deg , the crate begins to slide downward.

Question

A 45 kg crate is placed on an inclined ramp. When the angle the ramp makes with the horizontal is increased to 22 deg , the crate begins to slide downward. 
1-What is the coefficient of static friction between the crate and the ramp? 
2-At what angle does the crate begin to slide if its mass is doubled?

bobpursley · Answer

before sliding... frictionforce=gravitydownramp mg*mu*cosTheta=mg*sinTheta mu=tanTheta at the point of sliding. notice mass has nothing to do with the angle.