Remember that the equation for work is:
[tex]w = fd \cos( x) [/tex]
Where w = work, f = force, and x is the angle between the force and the direction of motion.
5000J is the amount of work, w, exerted. The distance, d, is 50m. x is 0 because the direction of motion is the same as the force (I'm assuming). Cos0 = 1. So you have:
[tex]5000 = (f)(50)(1)[/tex]
Just solve for f. F = 5000/50=100 N of force.
