what is angle of repose
The minimum angle of inclination of an inclined plane for which an object placed on the inclined surface just begins to slide is called angle of repose.
At angle of repose, the angle of inclination Q is such that w sinQ = f (f = frictional force) and the body begins to slide with zero acceleration.
And we know,
f = µ (w cosQ) [µ is the coefficient of friction]
w sinQ = µ w cosQ
= >tanQ = µ
= > Q = tan-1µ