4.     A block of mass 10 kg is being pushed down along an incline by an external force of 15N as shown in the figure. The incline is making an angle of 30o with the horizontal. Coefficient of kinetic friction between the block and the incline is 0.45.

        a.    (5 points)
               Draw a free body diagram for the block. Clearly show all forces acting on the block in your diagram.

    b.    (10 points)
            Calculate the normal force acting on the block by the incline, then calculate the frictional force. What are the directions of these forces?