Energy to drag a block

1. The problem statement, all variables and given/known data

whats the energy required to drag a block a distance L

2. Relevant equations

coefficiant of friction between block and floor = [tex]\mu[/tex]
density of block = p

force*distance = change in kinetic energy

3. The attempt at a solution

friction acting against movement Fr = [tex]\mu[/tex]mg m = mass of block

force in direction of movement F = ma

resultant force = F - Fr = m(a-[tex]\mu[/tex]g)

resultant force*L = energy = m(a-[tex]\mu[/tex]g)L

i dont think the last step is right though as im not sure sure that the assumption made that energy required is the same as the change in KE is correct...

help or guidance appreciated