A uniform board of length L and mass M lies near a boundary that separates two regions. In region 1, the coefficient of kinetic friction between the board and the surface is #, and in region 2, the coefficient is . The positive direction is shown in the figure. (Figure 1) Figure 1 Before: region 1 After: of 1 L fy f fl 1 region 2 W = Mgl ( + ) Correct This answer makes sense because it is as if the board spent half its time in region 1, and half in region 2, which on average, it in fact did. Part B What is the total work done by the external force in pulling the board from region 1 to region 2? (Again, assume that the board moves at constant velocity.) Express your answer in terms of M, g, L, , and . Wext =