Chapter 10: Q2P (page 260)
(I) What is the approximate mass of air in a living room 5.6× 3.6× 2.4m?
The mass of the air is 62.4 Kg.
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(II) If the base of an insect’s leg has a radius of about \(3.0 \times 1{0^{{\bf{ - }}5}}\;m\) and the insect’s mass is 0.016 g, would you expect the six-legged insect to remain on top of the water? Why or why not?
(I) State your mass and then estimate your volume. [Hint: Because you can swim on or just under the surface of the water in a swimming pool, you have a pretty good idea of your density.
What diameter must a \({\bf{15}}{\bf{.5}}\;{\bf{m}}\)-long air duct have if the ventilation and heating system is to replenish the air in a \({\bf{8}}{\bf{.0}}\;{\bf{m \times 14}}{\bf{.0}}\;{\bf{m \times 4}}{\bf{.0}}\;{\bf{m}}\) room every \({\bf{15}}{\bf{.0}}\;{\bf{min}}\)? Assume the pump can exert a gauge pressure of \({\bf{0}}{\bf{.710 \times 1}}{{\bf{0}}^{\bf{3}}}\;{\bf{atm}}\).
(II) The surface tension of a liquid can be determined by measuring the force \(F\) needed to just lift a circular platinum ring of radius \(r\) from the surface of the liquid. (a) Find a formula for \(\gamma \) in terms of \(F\) and \(r\). (b) At \(30^\circ C\), if \(F = 6.20 \times {10^{ - 3}}\;{\rm{N}}\) and \(r = 2.9\;{\rm{cm}}\), calculate \(\gamma \) for the tested liquid.
Water at a gauge pressure of \({\bf{3}}{\bf{.8}}\;{\bf{atm}}\) at street level flows into an office building at a speed of \({\bf{0}}{\bf{.78}}\;{\bf{m/s}}\) through a pipe \({\bf{5}}{\bf{.0}}\;{\bf{cm}}\)in diameter. The pipe tapers down to \({\bf{2}}{\bf{.8}}\;{\bf{cm}}\) in diameter by the top floor, \({\bf{16}}\;{\bf{m}}\) above (Fig. 10–53), where the faucet has been left open. Calculate the flow velocity and the gauge pressure in the pipe on the top floor. Assume no branch pipes and ignore viscosity.
Figure 10-53
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