**Third Examination
**

Physics 104

23 November 1982
#1. It requires ** 80 cal ** of heat energy to raise the temperature of
** 50 gm** of
a certain substance from ** 20 **^{o}C to ** 35 **^{o}C. The
substance has a molecular weight of ** 87 gm/mole**. Its specific heat [in
**
cal/(gm **^{o}C) ] is most nearly equal to

**Answer:**

#2. For the substance in problem **#1**, the molar specific heat [in **cal/(mole **^{o}K) ]
is most nearly equal to

**Answer:**

#3. Two metal rods, **A** and **B**, are joined end-to-end.
See sketch. They have equal cross-sectional areas. The left end of
rod **A** is kept at **100 **^{o}C by contact with boiling water,
while the right end of rod **B** is kept at **0 **^{o}C by contact
with an ice-water mixture. The thermal conductivity of rod **A** is 3
times that of **B**, but it is only half as long as **B**. After
steady state conditions have been reached, it is found that **3.5 gm** of ice
is melted every **7.0 minutes**. If the heat of fusion of ice is **80
cal/gm**, then the rate at which heat is conducted through the rods (in **cal/sec**)
is most nearly equal to

**Answer:**

#4. A weather balloon is filled with **9.00 m**^{3} of He
under a pressure of **1.05 atm**. It is released from the earth's
surface, where the temperature is **90 **^{o}F. The balloon
rises to an altitude where the temperature is **-5 **^{o}F and the
pressure of the He is **0.95 atm**. The volume [in **m**^{3}]
of the Helium balloon is most nearly equal to

**Answer:**

#5. A Gas begins with a pressure of ** 8.0 ´ 10**^{5}
Pa, a volume of **0.0100 m**^{3}, and a temperature of **400 **^{o}K.
It expands isothermally to a volume of **0.0800 m**^{3}.
The work (in **Joules**) done **by** the gas is most nearly equal to

**Answer:**

#6. Oxygen molecules have a molecular weight of **32 amu**. At
room temperature (**20 **^{o}C) the average translational kinetic
energy ( in **Joules**) of oxygen molecules is most nearly equal to

**Answer:**

#7. A gas undergoes the processes indicated by the path in the **p-V** diagram **ABCA**. The
work (in **Joules**) done **by** the gas during one cycle is most nearly equal to

**Answer:**

#8. In problem **#7**, the heat (in **cal**) **removed** from the gas
during one cycle, **ABCA**, is most nearly equal to
**Answer:**

#9. **Two moles **of an ideal, diatomic gas undergoes an increase in
temperature by **40 **^{o}K, isobarically. The heat energy
added to the gas is most nearly equal to
( **R **= ideal gas constant)

**Answer:**

#10. For the gas in problem **#9**, the work done **by** the gas is most
nearly equal to
**Answer:**

#11. A fixed amount of gas with
** g = 1.50**, pressure of ** 6.0 atm**. and volume of
** 1.0 liter** is expanded
adiabatically to a volume of ** 4.0 liter**. The pressure (in **atm**) of
the gas is then most nearly equal to
**Answer:**

#12. Nitrogen molecules have a diameter of ** 3.2 ´ 10**^{-8} cm.
At a low pressure in the container, the density of nitrogen is **2.4 ´ 10**^{16}
molecules/cm^{3} , and the rms speed is **2.0 ´ 10**^{5}
cm/sec. The number of collisions per second which nitrogen molecules
undergo is most nearly equal to
**Answer**

#13. A hole is drilled through the earth's crust to a depth where the
temperature is **700 **^{o}C. A liquid is circulated to this
depth and is brought back to the surface as a gas at a temperature of **600**^{o}C.
The gas then does work in an engine where it is exhausted at **120**^{o}C.
The theoretical efficiency of the engine
is

14. An engine burns fuel (**6000 cal/gm**) at the rate of **4.0 gm/min**.
The temperature of its working substance is **500 **^{o}K before
delivering its energy to the engine, and it is exhausted from the engine at **350
**^{o}K. The maximum theoretical power (in **watts**)
generated by the engine is most nearly equal to

**Answer:**

#15. During the isothermal expansion (T = **400 **^{o}K) in a
Carnot engine, **440 cal** of heat is absorbed by the working substance, and **330
cal** is rejected during the isothermal compression at **300 **^{o}K.
The change in entropy ( in **cal/**^{o}K) of the working substance
during one cycle is most nearly equal to
**Answer:**