TERMODIN ´
AMICA
LISTA DE EJERCICIOS No1
WILLIAM OSWALDO SOSA CORREA
Universidad Pedag´ogica y tecnol´ogica de Colombia.
1. Un soldador llena un tanque de 0.0750
m3con ox´ıgeno (masa molar = 32.0
g/mol) a una presi´on manom´etrica de
3,00×105Pa y una temperatura de 37.0
0C. El tanque tiene una fuga, y con el
tiempo se escapa algo de ox´ıgeno. Cier-
to d´ıa en que la temperatura es de 22.0
0C, la presi´on manom´etrica del ox´ıgeno
en el tanque es de 1,80×105. Calcule: a)
La masa inicial de ox´ıgeno; b) la masa
que se fug´o. m3
2. A una altura de 11,000 m (altura de cru-
cero t´ıpica de un jet comercial), la tem-
peratura del aire es de — 56.50Cy su
densidad es de 0.364 kg/m3. Determine
la presi´on de la atm´osfera a esa altura.
(La temperatura a esta altura no es la
misma que en la superficie).
3. At a time of 100000 years after the first
instant of the Big Bang at the begin-
ning of the Universe, the temperature
was about 1,0×104K, and the density
of the hot gas filling the Universe was
about 1,0×10−16 kg/m3. By mass, this
gas con- sisted of 75 % H atoms (not mo-
lecules) and 25 % He atoms. (a) Calcu-
late the number of atoms per unit vo-
lume. (b) Calculate the pressure contri-
buted by these atoms. (c) Calculate the
rms speed of the H atoms and of the He
atoms.
4. The Mediterranean loses a large volume
of water by evaporation. The loss is ma-
de good, in part, by currents flowing into
the Mediterranean through the straits
joining it to the Atlantic Ocean and the
Black Sea. Calculate the rate of evapora-
tion (in km3/h) of the Mediterranean on
a clear summer day from the following
data: the area of the Mediterranean is
2,9×106km2, the power per unit area
supplied by sunlight is 1,0×103W/m2,
and the heat of vaporization of water is
2,43 ×106J/kg (at a temperature of 21
0C). Assume that all the heat of sunlight
is used for evaporation.
5. A glass mug has a mass of 125 g when
empty. It contains 180 g of coffee, and
both the mug and the coffee are at 70
0C. You add 15 g of cream at 5 0Cto
the coffee. Assuming the mugcoffee sys-
tem is isolated, find the common final
temperature. Assume that coffee has the
same specific heat as water and that the
cream has a specific heat of 2900 J/kg.
0C.
6. The pendulum (rod and bob) of a pen-
dulum clock is made of brass. (a) What
will be the fractional increment in the
length (∆L/L) of this pendulum if the
temperature increases by 20 0C? What
will be the fractional increase in the
period of the pendulum? (b) The pen-
dulum clock keeps good time when its
tempera- ture is 15 0C. How much time
(in seconds per day) will the clock lose
when its temperature is 35 0C?
7. A simple gadget for heating water for
showers consists of a black plastic bag
holding 10 liters of water. When hung
in the sun, the bag absorbs heat. On a
clear, sunny day, the power delivered by
sunlight per unit area facing the Sun is
1,0×103W/m2. The bag has an area of
0.10 m2facing the Sun. How long does
it take for the water to warm from 20
