So we want to know how much work against the force of gravity is done by a workman that carries a sheet of plywood with a mass m=8 kg up the ramp that has a length of l= 3 m and at an angle α= 20°. The formula for work is W=F*s where F is the force and s is the distance. Since the force of gravity is perpendicular to the ground, the workman is doing the work against gravity only in the direction perpendicular to the ground. So s=l*sin(α)=3*sin(20)=3*0.342=1.026m. So the work is: W=m*g*s=8*9.81*1.026=80.52048 J. So the work done against gravity by the workman is W=80.52 J.
