433_Physics ProblemsTechnical Physics

433_Physics ProblemsTechnical Physics - Chapter 14 P14.71...

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Chapter 14 435 P14.71 Note : Variation of atmospheric pressure with altitude is included in this solution. Because of the small distances involved, this effect is unimportant in the final answers. (a) Consider the pressure at points A and B in part (b) of the figure: Using the left tube: PP g h g L h Aa w =+ + atm ρ af where the second term is due to the variation of air pressure with altitude. Using the right tube: g L B atm 0 But Pascal’s principle says that AB = . Therefore, Pg L h g L h aw atm atm += ++ ρρ 0 or wa w hL −= bg 0 , giving w = F H G I K J = F H G I K J = 0 1000 750 1000 129 500 125 . .. cm cm (b) Consider part (c) of the diagram showing the situation when the air flow over the left tube equalizes the fluid levels in the two tubes. First, apply Bernoulli’s equation to points A and B yy vv v A B == = ,, a n d 0 This gives: Pv g y P g y Aa a A Ba a B ++= + + 1 2 1 2 0 2 2 and since = , this reduces to:
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