91Ó°ÊÓ

Professor Gordon Holloway and his students at the University of New Brunswick went to a fast-food emporium and tried to drink chocolate shakes \(\left(\rho \approx 1200 \mathrm{kg} / \mathrm{m}^{3}, \mu\right.\) \(=6 \mathrm{kg} / \mathrm{m}-\mathrm{s}\) ) through fat straws \(8 \mathrm{mm}\) in diameter and \(30 \mathrm{cm}\) long. (a) Verify that their human lungs, which can develop approximately 3000 Pa of vacuum pressure would be unable to drink the milkshake through the vertical straw. (b) A student cut \(15 \mathrm{cm}\) from his straw and proceeded to drink happily. What rate of milkshake flow was produced by this strategy?

Water at \(20^{\circ} \mathrm{C}\). Aws by gravity through a smooth pipe from one reservoir to a lower one. The elevation difference is \(60 \mathrm{m}\). The pipe is \(360 \mathrm{m}\) long, with a diameter of \(12 \mathrm{cm} .\) Calculate the expected flow rate in \(\mathrm{m}^{3} / \mathrm{h}\). Neglect minor losses.

A garden hose is to be used as the return line in a waterfall display at a mall. In order to select the proper pump, you need to know the roughness height inside the garden hose. Unfortunately, roughness information is not supplied by the hose manufacturer. So you devise a simple experiment to measure the roughness. The hose is attached to the drain of an above-ground swimming pool, the surface of which is \(3.0 \mathrm{m}\) above the hose outlet. You estimate the minor loss coefficient of the entrance region as \(0.5,\) and the drain valve has a minor loss equivalent length of 200 diameters when fully open. Using a bucket and stopwatch, you open the valve and measure the flow rate to be \(2.0 \times\) \(10^{-4} \mathrm{m}^{3} / \mathrm{s}\) for a hose that is \(10.0 \mathrm{m}\) long and has an inside diameter of \(1.50 \mathrm{cm} .\) Estimate the roughness height in \(\mathrm{mm}\) inside the hose.