How Do Work-Energy Principles Apply When Potential Energy Changes?

[henry3369]

(1) Wnet = ΔK
(2) Wnc = ΔE

1. Is equation (1) always correct even if the potential energy of the object is also changing? A
2. Is equation (2) always going to have a small value than Wnet? And is Wnc always 0 if Wnet is zero?

 

[Doc Al]

1. Is equation (1) always correct even if the potential energy of the object is also changing?

Yes, as long as you include the work done by ALL forces acting. This is the so-called "work-energy" theorem. (There are some subtleties, which I won't confuse you with.)

2. Is equation (2) always going to have a small value than Wnet?

No.

And is Wnc always 0 if Wnet is zero?

No.

Example: Imagine a block sliding down an incline at constant speed. (Friction is obviously acting.) The net work including all forces will be zero. But the work done by friction (the non-conservative force in this example) will not be zero.