A particle has 37.5 J of kinetic energy and 12.5 J of gravitational potential energy at one point during its fall from a tree to the ground. An instant before striking the ground, how much mechanical energy-rounded to the nearest Joule-does the particle have? Ignore air resistance.​

50J

Explanation:

Mechanical energy follows the same principles of kinetic energy and potential energy, it is conserved. So Ei = Ef.

Mechanical energy is the sum of ALL energy's. There is no friction, so its just kinetic plus potential.

37.5 + 12.5 = 50J

Since the particle has not touched the ground, it has not transferred any energy to the ground yet, therefore the mechanical energy must still be 50J; mostly in kinetic energy with a very small amount of potential because of the low height relative to the ground.