You and a friend each apply 500 N of force to move a cement block 50 cm. How much work was done on the cement block?

 W = 500 J

Explanation:

Work is defined by

         W = F . x

if we develop the dot product

         W = F x cos θ

where is the angle between the force and the displacement, in this case the angle is zero, so cos 0 = 1

          W = F x

indicate that each person applies a force of 500 N, so the total force is

         F = 1000 N

let's reduce the distance to the SI system

          x = 50 cm = 0.50 m

let's calculate

          W = 1000 0.50

          W = 500 J