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
socalled 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— : 3.43x103z+ 1 t= .
55.56 97.2 191 ...
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 Spring '08
 Pitaressi

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