A body projected vertically upwards from Earth reaches a maximum height equal to Earth’s radius and returns. At which instant is the power exerted by gravity greatest?
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A body projected vertically upwards from Earth reaches a maximum height equal to Earth’s radius and returns. At which instant is the power exerted by gravity greatest?

G1 Physics · Accepted Answer

Step 1: Instantaneous power is P=Fv cosθ. Gravity acts downward. Step 2: During ascent P is negative, at the top zero, and on descent positive. Just before impact gravity and speed give the maximum positive power. Final answer: A — Just before the body hits Earth.