Answer
1) a
2) a and c
Work Step by Step
Mechanical energy is conserved only when the only forces acting on the object are conservative, making a) the correct answer. Overall energy in the system is conserved when no work is done on the system, and this occurs in cases a and c. NOTE: energy in the universe is ALWAYS conserved. They say the systems are isolated in a and c to specify that there is no energy lost to surroundings.
