Question

The block b moves with a velocity u relative to the wedge a. if the velocity of the wedge is c as shown in figure

Answer 1

velocity of the block B is u wrt  the wedge.
velocity of the wedge A  wrt to stationary frame:  c

case 1:   vectors u and c are in the same direction.
              => absolute velocity of the block = u + c in the same direction.

case 2:  vectors u and c are in the opposite direction.
              => abs  velocity of the block = u - c

case 3:  vectors  u and  c are perpendicular to each other:
              => abs. velocity of the block = √(u² + c²)