Physics for Scientists and Engineers: A Strategic Approach with Modern Physics (3rd Edition)

Published by Pearson
ISBN 10: 0321740904
ISBN 13: 978-0-32174-090-8

Chapter 19 - Heat Engines and Refrigerators - Exercises and Problems - Page 554: 70

Answer

See the detailed answer below.

Work Step by Step

a) We can see that the volume of system 1 is constant while the pressure of system 2 is constant. Gas 1 undergoes an isochoric process while gas 2 undergoes an isobaric process. And since the system, gas 1 and gas 2, is isolated, the heat lost from 1 is gained by 2. $$Q_1+Q_2=0$$ $$n_1C_{\rm V}\Delta T_1+n_2C_{\rm P}\Delta T_2=0$$ The two gases are helium which is a monatomic gas, so $$\frac{3}{ \color{red}{\bf\not}2}n_1 \color{red}{\bf\not}R(T_f-T_{i1})+ \frac{5}{\color{red}{\bf\not}2}n_2 \color{red}{\bf\not}R(T_f-T_{i2})=0$$ $$ 3n_1 (T_f-T_{i1})+ 5n_2 (T_f-T_{i2})=0$$ $$ 3n_1 T_f-3n_1 T_{i1}+ 5n_2 T_f-5n_2 T_{i2}=0$$ $$ 3n_1 T_f+ 5n_2 T_f=3n_1 T_{i1}+5n_2 T_{i2}$$ $$ (3n_1 + 5n_2) T_f=3n_1 T_{i1}+5n_2 T_{i2}$$ $$ T_f=\dfrac{3n_1 T_{i1}+5n_2 T_{i2}}{3n_1 + 5n_2}$$ $$ T_f=\dfrac{3(0.06)(600)+5(0.03)(300)}{3 (0.06)+ 5(0.03)}$$ $$T_f=\color{red}{\bf 464}\;\rm K$$ ____________________________________________________ b) The heat transferred from the left side to the right side is heat gained by gas 2, which is given by $$Q_2=\frac{5}{2}n_2R(T_f-T_{i2})$$ $$Q_2=\frac{5}{2}(0.03)(8.31)(464-300)$$ $$Q_2=\color{red}{\bf 102}\;\rm J$$ ____________________________________________________ c) We know that gas 2 undergoes an isobaric process, so $$\dfrac{V_i}{T_i}=\dfrac{V_f}{T_f}$$ where $V_f=V_i+\Delta V$ $$\dfrac{V_i}{T_i}=\dfrac{V_i+\Delta V}{T_f}\tag 1$$ Now we need to find $V_1$ and since we know $n$ and $T_i$, we need to find $P_i$ of gas 2. (In this part we are working on gas 2 only). Since the piston of gas 2 was initially at rest, the initial pressure of gas 2 is given $$P_{i}=P_a+P_{piston}=P_a+\dfrac{mg}{A}$$ where $m$ is the mass of the piston and $A$ is its cross-sectional area. $$P_{i}=(1.013\times 10^5)+\dfrac{(2)(9.8)}{\pi \times 0.05^2}=\bf 1.038\times 10^5\;\rm Pa$$ Thus the initial volume $$V_i=\dfrac{nRT_i}{P_i}=\dfrac{(0.03)(8.31)(300)}{1.038\times 10^5}$$ $$V_i=\bf 750.52\;\rm cm^3$$ Plugging into (1); $$\dfrac{750.52}{300}=\dfrac{750.52+\Delta V}{464} $$ Hence, $$\Delta V=Ah=\dfrac{(750.52)(464)}{300}-750.52=\bf 410.284\;\rm cm^3$$ $$ h= \dfrac{410.284}{A} = \dfrac{410.284}{A} = \dfrac{410.284}{\pi (5)^2} $$ $$h=\color{red}{\bf 5.2}\;\rm cm$$ ____________________________________________________ d) The fraction of geat that converted to work is given by $$\dfrac{W}{Q}=\dfrac{\text{ Area under the $P_V$}}{Q}=\dfrac{P\Delta V}{Q}$$ $$\dfrac{W}{Q}=\dfrac{(1.038\times 10^5)(410.284\times 10^{-6})}{102}=\color{red}{\bf 0.42}$$ Hence, $$\boxed{W=0.42Q}$$
Update this answer!

You can help us out by revising, improving and updating this answer.

Update this answer

After you claim an answer you’ll have 24 hours to send in a draft. An editor will review the submission and either publish your submission or provide feedback.