Sunlight near the earth has an intensity of about 1500W/m². Find the force which sunlight exerts when it reflects from a square meter of mylar solar sail.

The force is given by the change in momentum per unit time, so find the momentum change in one second.

In one second, each square meter of surface reflects 1500J of energy which carries momentum 1500J/c

The photons reverse their direction, so the momentum change and thus the force on one square meter is 2×1500J/c = 3000/3×10⁸N = 10^-5N.

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