Question

N5D.4 (e) and (f)

both sides of the x component of Newton's second lav v, and take the indefinite integral of both sides.) Rich- N5D.4 We have seen that the drag force between a fluid and an object moving through that fluid is proportional to 2 if the object is big and/or fast and/or the fluid is not a m ery viscous but is proportional to löl if the object is small Slo At kin d/or slow and/or the fluid is very viscous. But how can you really tell what formula to use? It turns out that you can tell by calculating a unitless constant physicists call an a object's Reynolds number. We define this number to be N5 (N5.20) where L expresses the object's size (it does not really mat- ter much if this is the object's length, width, or depth), and vis the fluid's kinematic viscosity (v 13 x 10-6 m2/s for air, 1.0 × 10-6 m2/s for water, 76 × 10-6 m2/s for honey, all at room temperature and standard pressure). The approx- imate rule is that if Re 1000, then | FolxI and if Res1, then | FD | χ . Between those values, neither formula works very well a) Consider a basehall 0075 ml moing at 20 l N5 Linearly Constrained Motiorn (e) Consider a bumblebee moving a few centimeters per very well nderstand -sectional second through air. Will either formula work very well for this case? sor ons hro agh ati ill elerate all he object (N5.18) maller its speed. (D You may find it surprising that the kinematic viscos- ity of air is larger than that for water. However, what we usually think colloquially of as "viscosity" is the dynamic viscosity μ, which more directly expresses say, the force you would have to exert to drag a fin- ger through the fluid. These quantities are related by the fluid density ρ: μ ρν. What is the ratio of the dynamic viscosities of water and air? ithout voly- N5D.5 At highway speeds, the drag force exerted by air on a moving car dominates over other forms of friction. a (a) Show that the power the engine must produce to make 1g up for the work done by the drag force on the car proportional to la 3 h this iven L

Answer 1

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