Physics: Principles with Applications (7th Edition)

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

Chapter 15 - The Laws of Thermodynamics - Problems - Page 439: 28

Answer

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Work Step by Step

a. Find the work done per second from the information about the engine. $$\frac{W}{t}=(180\frac{J}{cycle \cdot cylinder})(4\;cylinders)(25\frac{cycles}{s})=1.8\times10^4 J/s$$ b. The efficiency is given by equation 15–4a. $$e=\frac{W}{Q_H}$$ Find the heat input per second. $$Q_H=\frac{W}{e}$$ $$Q_H/t=\frac{W/t}{e}=\frac{1.8\times10^4 J/s }{0.22}=8.2\times10^4 J/s $$ c. To find out how long a gallon lasts, divide the energy contained in a gallon of gasoline by the rate at which the energy is being used. $$\frac{130\times10^6 J}{8.182\times10^4 J/s }=1589s\approx 26\;min$$
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