An 100kg box is placed on the ramp. As one end on the ramp is raised the box begin to move down ward just as the angle of inclination reaches 15 degree . What the coeffenict of static friction between box and ramp .. ?

Answer 1

ma=mgsinα-F(fr)=mgsinα-μN=
=mgsinα-μmgcosα

μ(stat.fr) => a=0

0= mgsinα-μmgcosα
μ=tanα