# Energy Transfer and Work in Action-Reaction Forces [closed]

simple but confusing for me. I hope this question doesn't close or disappear. Questions continue to arise about work and energy.

Situation Description

1. A and B exert forces on each other and do work.

2. When I push an object with a force of 10N for 5m, I do 50J of work, and the object's kinetic energy increases by 50J.

3. The object also exerts a force of 10N in the opposite direction on me, doing -50J of work. Therefore, the work I do on the object is Wab = 50J (Fab * d), and the work the object does on me is Wba = -50J (Fba * d).

4. It is assumed that A and B move stick together.(so Fab=-Fba and d is same)

Question Points

1. The work I do on the object increases the object's kinetic energy, and the work the object does on me (the reaction force) decreases my kinetic energy.

2. The work the object does on me is negative work, meaning the object takes energy from me.

3. Why can't we simply add the work done by the action force and the work taken by the reaction force when calculating the total kinetic energy change of the object?

4. Why doesn’t the total kinetic energy change of the object become 100J when adding the work I do on the object and the work the object does on me?

• Work is a type of energy transfer from system A to system B. It’s not clear why you’d add the magnitudes, as they apply to different systems; perhaps you could clarify your question. If I owe you \$50—meaning you’re owed \$50 from me—is there any reason to discuss the amount of \$50+\$50=\\$100? Commented Jul 10 at 2:32
• @Chemomechanics It is confusing that the work A does on B and the work B does on A are not always equal in magnitude and opposite in sign. For example, even if A does 50J of work on B, the work B does on A might not be -50J; it could be a different value, even positive. In other words, generally, Wab is not equal to -Wba. Returning to the original situation, if A and B each exchange 50J of energy, your analogy is perfect. However, I am unsure how to interpret the situation when the initial conditions are changed so that Wab is not equal to -Wba. Commented Jul 10 at 2:58
• Again, please consider clarifying your question; it's currently about a magnitude of 50 J of work done on one body and a magnitude of 50 J of work done on another body. If you have a different scenario in mind, please describe it clearly. Commented Jul 10 at 3:50