Two objects interact with each other and with no other objects.Initially object A has a speed of 5 m/s and object B has a speed of 10 m/s.In the course of their motion they return to their initial positions.Then A has a speed of 4 m/s and B has a speed of 7 m/s.We can conclude:
A)the potential energy changed from the beginning to the end of the trip
B)mechanical energy was increased by nonconservative forces
C)mechanical energy was decreased by nonconservative forces
D)mechanical energy was increased by conservative forces
E)mechanical energy was decreased by conservative forces

Question

Quizplus · Accepted Answer

According to the law of conservation of energy, the total mechanical energy of a system remains constant if the only forces acting on the system are conservative forces. In this case, the objects return to their initial positions, so there is no change in height and therefore no change in gravitational potential energy. Since the mechanical energy decreased, it must have been due to nonconservative forces, such as friction or air resistance, which caused some energy to be lost as internal energy or heat.

Two Objects Interact with Each Other and with No Other