Unformatted text preview: Chapt. 15 Fluids 141 very approximate, and so any values calculated using them will be likewise approximate. Also uncertainties tend to be large for the difference of nearly equal values. a) Consider the xdirection forces on one hemisphere (the one that’s roundy in the positive xdirection). Four forces act: the external air force, the internal air force (the vacuum’s not complete), the normal force of the rim of the other hemisphere, and the pull force of the horses. For equilibrium 0 = F int + F ext + F N + F horse . Note that the internal pressure force in the xdirection on a differential bit of sphere area dA is dF int = P int dA ˆ n · ˆ x , where ˆ n is the normal to the surface area. A bit of insight shows that F int = P int πR 2 , where R is the radius of the hemisphere. What is the expression for F ext in terms of external pressure? Get the sign of F ext right. b) Given R = 0 . 5 ft (ft is foots, foots), P ext = 1 . 01 × 10 5 Pa, and F horse = 7500 N, what is P int ? Assume the hemispheres have negligible thickness.?...
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 Fall '06
 Buchler
 Physics, Centrifugal Force, Force, Von Guericke, FINT, external air pressure

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