Question

a student pushes a 40-N block across the floor for a distance 0f 10 m how much work was done to move the block?

Answer 1

W=f*d
= 40N * 10m
work= 400 joules

Answer 2

We don't know how much force s/he had to use to push the block.
If the floor was smooth and wet, it needed very little force.
If there was sandpaper or stones on the floor, it took a lot of force.

Whatever amount of force s/he needed to use, the work done was

          Work  =  (amount of force, in Newtons) x (10 m)

          The unit is Joules.