The work done by gravity is equal to the change in the potential energy of a given raindrop and it can be determined by the formula: A = En = m * g * h, where m is the mass of the drop (m = 20 mg = 20 * 10 ^ -6 kg) ; g – acceleration due to gravity (reference value, g ≈ 10 m / s2); h is the initial drop height (h = 2 km = 2000 m).
Let’s make a calculation: A = m * g * h = 20 * 10 ^ -6 * 10 * 2000 = 0.4 J.
Answer: When a drop fell, gravity did a work of 0.4 J.
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