Drag Force and Terminal Velocity Problems
Fishbane Chp 5
Q33. Consider Eq. (5–32) for the drag force, which has two terms. Which term, if any,
dominates at low speeds and which, if any, dominates at high speeds? How would you
decide the size of the domains for which one term is much larger than the other?
P37. Estimate the drag force on an automobile cruising at 65 mi h . Assume that the drag
coefficient CD is 0.45 and that the car’s cross-sectional area is 4 m . Take air to
have a density of 125 kg m .
P38. A parachute is rigged so that a parachutist of total mass 116 kg with full gear
reaches the ground at a terminal speed of 4.9 m s . Assuming that the drag force on
the parachutist, moving with speed v, has a magnitude equal to kv , what is the
value of k?
P40. A race car of mass 800 kg has a maximum acceleration from rest of 4.8 m s .
Assume that the car’s engine is such that the force on the tires is constant and that the
car’s effective cross-sectional area into the air is 18 m . If the car’s top speed is
observed to be 90 m s , what is its drag coefficient CD ? Take the density of air as
125 kg m3 .
P44. Assume that the drag force on a parachute is given by Eq. (5–30) in the text. The
effective area of the parachute is 30 m and the density of air is 125 kg m . If a 90-
kg parachutist finds that his terminal speed is 6.0 m s , what is the drag coefficient?
P45. A parachutist of 60-kg mass uses a parachute similar to the one used by the
parachutist of the previous problem. Determine the terminal speed of this lighter