4. What are the input and output of a bicycle system? O A. The input is pushing on the pedals and the output is the bike moving. OB. The input is the bike moving and the output is the bike stopping. C. The input is the bike moving and the output is the wheels turning.

The drag force, fd, imposed by the surrounding air on a vehicle moving with velocity v is given by fd = cdaρv 2/2 where cd is a constant called the drag coefficient, a is the projected frontal area of the vehicle, and ρ is the air density. an automobile is moving at v = 80 kilometers per hour with cd = 0.28, a = 2.3 m2, and ρ = 1.2 kg/m3.