Question

If a bicyclist doubles his speed, how much more force must he apply to overcome air resistance (drag)?

Answer 1

Drag force, Fd = 1/2ACv²
Where is the density of air, A is the area of the cyclist, C is the drag coefficient and v is the velocity of the cyclist.
Fd = Kv²
Where K is a constant, K = 1/2AC

When v is doubled,
F'd = K(2v)²
4 Kv²
= 4 Fd
So the force increases by four times.