In which of the following situations is mechanical energy conserved a. a car rolls downhill b. a person swims through the water c. a collision between two cars d. hey ball is thrown up into the air without encountering air resistance

Correct answer is option D(D. Hey ball is thrown up into the air without encountering Air resistance)

Explanation:

Law of conservation of energy: According to law of conservation of energy, Energy can neither be credited nor it cannot be destroyed only it can transfer from one form of energy to another form of energy.

Law of Conservation of mechanical energy

According to Law of Conservation of Mechanical energy, in a closed system in the absence of dissipation forces like friction force or air resistance, total amount of mechanical energy,  remains constant.

For example, in the absence of air resistance when a ball is thrown up into the air under gravitational field of earth, then mechanical energy of ball will remains conserved.

Therefore mechanical energy of Hey ball which is thrown up into the air without encountering Air resistance will remain conserved