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how18soln

# how18soln - Integrate When I = When you study ﬂuid...

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Unformatted text preview: Integrate When I = When you study ﬂuid mechanics you will learn that the drag D on a body when moving through a fluid with mass density p is given as 2 Can2 A where V15 the velocity of the body rela— tive to the ﬂuid; A is the frontal area of the object; and C is the so-called coeﬁieiem ofdrag usually determined by experiment. A racing plane on landing is moving at a speed of 350 krnlhr when a braking parachute is deployed. This parachute has a frontal area of 30 m2 and a CID = 1.2. The plane has a frontal area of 20 m2 and a C1) = 0.4. lfthe plane and parachute have a com- bined mass of 8 Mg. how long does it take to go from 350 krn/hr to 200 km/hr by just coasting? Take p = l.2475 ngm3 and neglect rolling resistance from the tires. There is no wind. = %(1.2475)(V2)[(1.2)(30) + (.4)(20)] de malt 3 dV dt £1: -2745 V2 8x103 = — 27.45 V2 — 27.45 V2 dt - v“ = —3.43 x10'3t + C1 1000 3600 =———350 =97.2 m/s c. . -2 97.2 i = 3.43 x10’3t+ 1 V 97.2 1000 3600 =200——— =55.56 m/s = 27.45 V2 _1— : 3.43x10-3z+ 1 t= . 55.56 97.2 191 ...
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