Answer: 400 joules.
Explanation:
The minimal force needed to lift a 100N block is a force of 100N.
Now, work is defined as a movement done by a force, so we can write the work as:
W = F*d where F is the force and d is the distance traveled, in this case d = 4m so we have:
W = 100N*4m = 400 joules
