Given the mass of block is m, velocity of the elevator is υ, inclination of the wedge is θ. Let the distance travelled by the elevator in time t be d, which is d = u× t Now by drawing the F.B.D of the block, we have friction force f = Also the angle between the elevator displacement and the frictional force is 90-θ So, as per the definition of work, the work done by the frictional force on the lock is = f× d W = f× d = m× g× × u× t× =