Energy is the capacity of doing work
<h2>The man have to apply force of 160 N</h2>
Explanation:
The work done to lift the bag of weight mg through height 2.5 m is 400 J
The work done can be found by relation W = mg x h
Thus mg = = = 160 N
Therefore the man have to apply the force of 160 N
You are trying to convert mass to volume. That ain't working