Select the situations from the list in which mechanical energy is conserved. (a) a ball slides down a hill with friction. (b) an ice skater glides along the ice. (c) a ball is dropped from a certain height and bounces back to a lower height.(d) a child swings on a frictionless swing, ignoring air resistance. (e) a ball slides down a frictionless hill. (f) the moon orbits the earth.

B, D,E,F

Explanation:

Situations from the list in which mechanical energy is conserved.

Whenever there is friction there is always some loss of energy in the process and hence energy cannot be conserved.

- The Moon orbiting the Earth  (Total energy is remains the same)

- An ice skater gliding along the ice ( smooth surface no friction loss)

- A ball sliding down a friction less hill  ( again friction less process)

- A child swinging on a friction less swing, ignoring air resistance

Out of the options provided, the situations in which mechanical energy is conserved are:

This implies the correct answers are B, D, E, and F.

B, "As the moon orbiting the earth", its total mechanical energy will be the same because no external forces can act on it whether it moves in an elliptical or circular way.

D, "An ice skater gliding along the ice": the mechanical energy is conserved in this situation since there are no dissipative forces (no friction loss)

E, "A ball sliding down a frictionless hill": mechanical energy is also conserved in this situation because there are no dissipative forces (No friction or air resistance) and it remains constant

F, "A child swinging on a frictionless swing, ignoring air resistance": mechanical energy is also conserved in this situation due to no friction and air resistance.

The law of conservation of mechanical energy suggests that the total amount of mechanical energy, which is the total sum of an object kinetic and potential energy, in a closed system is constant when there are no dissipative forces (friction, air resistance, etc.)

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