The magnitude of the drag force of air resistance on a certain 20kg object is proportional to its speed. if the object has a terminal speed 80m/s, what is the magnitude of the drag force of an object when it is falling with a speed 30m/s?

Given:
object = 20kg
terminal speed of object = 80 m/s

According to the problem, drag force is proportional to speed, so Fd = kv ; k is some constant
At terminal velocity Vt: Fg = Fdmg = kVtk = mg / Vt = (20.0)(9.8)/(80.0) = 2.45 kg/s
Fd = kv = 2.45v
Fd = 2.45 (30.0) = 73.5 N

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