The net vertical force on a box F as a function of the vertical position y is shown below.

W = 0 J

Explanation:

Formula for work done is;

W = F × d

Where;

W is work done

F is Force

d is distance covered

What this means is that we will calculate the area under which the given times in the graph pass.

Thus;

At constant force of F = 40 N which falls in between distance of 0 m and 2m,

W1 = 40 × 2 = 80 J

At constant force of -20 n which will fall between distance of 2 m and 6 m which is 4m, we have;

W2 = -20 × 4

W2 = -80 J

Thus, total workdone is;

W = W1 + W2

W = 80 - 80

W = 0 J

a and b sometimes have a positive value