Which one of the following is correct? * A. Average speed and average velocity are the same.

B. There is no difference between uniform motion and uniformly accelerated motion.

C. Acceleration is the rate of change of speed.

D. Uniformly accelerated motion is a motion with constant acceleration.

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.