Physics: Principles with Applications (7th Edition)

Published by Pearson
ISBN 10: 0-32162-592-7
ISBN 13: 978-0-32162-592-2

Chapter 10 - Fluids - General Problems - Page 289: 73

Answer

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Work Step by Step

a. The fluid is confined and the pressures are equal. Apply Pascal’s principle. $$\frac{F_{plunger}}{A_{plunger}}=\frac{F_{needle}}{A_{needle}}$$ $$ F_{needle}=F_{plunger} \frac{A_{needle}}{A_{plunger}}$$ $$ F_{needle}=(3.2\;N) \frac{\pi (0.10\times10^{-3}m)^2}{\pi (0.65\times10^{-2}m)^2}=7.6\times 10^{-4}\;N$$ b. Find the plunger force. $$F_{plunger}=P_{plunger}A_{plunger}=(75\;mm-Hg)(\frac{133\;N/m^2}{1\;mm-Hg})\pi(0.65\times10^{-2}m)^2=1.3\;N $$
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