. It is known that the static-friction force between the small block B and the plate will be exceeded and that the block will start sliding on the plate when the total acceleration of the block reaches 4 m/s2 . If the plate starts from rest at t = 0 and is accelerated at the constant rate of 5 rad/s2 , determine the time t and the angular velocity of the plate when the block starts sliding, assuming r = 250 mm.