A rough plane is inclined to the horizontal at an angle α\alphaα. A block of mass m m\,m kg is placed on the plane and remains in equilibrium, on the point of sliding down the plane.
The coefficient of friction between the block and the plane is 0.15.
Find the value of α\alphaα.
The block is now projected with speed 0.4 m s−1^{-1}−1 down a line of greatest slope of the plane. Describe the subsequent motion of the block, giving a reason for your answer.