Two objects interact with each other and with no other objects. Initially object A has a speed of $5\frac{m}{s}$ and object $B$ has a speed of $10\frac{m}{s}.$ In the course of their motion they return to their initial positions. Then A has a speed of $4\frac{m}{s}$ and $B$ has a speed of $7\frac{m}{s}.$ We can conclude:

$$

mechanical energy was increased by nonconservative forces

mechanical energy was decreased by conservative forces

the potential energy changed from the beginning to the end of the trip

mechanical energy was increased by conservative forces

mechanical energy was decreased by nonconservative forces