Answer:
60 J
Explanation:
Given,
Work done to push the box = 100 J
Energy dissipated by friction = 40 J.
According to work energy theorem work done is equal to change in kinetic energy.
Change in Kinetic energy = Work done by student + Work done by friction
Change in Kinetic energy = 100 J - 40 J
Work done by the friction will be negative because it will act in opposite direction of force applied.
Change in Kinetic energy = 60 J