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A man of mass 70 kg is in free fall in the air. He reaches a terminal speed of about v_term = 54 m/s. (Note that v_term >> v_crit and we are in the pressure dominated regime where F_fric is directly propotional to v^2 ; we have g = 9.8 m/s )

What is the force (in N) due to air-drag on the man?

at a constant speed, there is no acceleration, so no net force. The upward force = weight = 9.8*70

First calculate C_2 = (mg / (v^2 * r^2) where r is unknown, then calculate F = C_2 * r^2 * v^2
I presume this question is from Walter Lewin's Physics course

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