PHYS 201 TEST
#4 11/26/08 DR. HOLMES NAME
Do all eight problems. The worth of each
problem is marked beside the space for the answer. All answers should be in MKS
units unless otherwise indicated. Show your work for partial credit. Work
should be under the problem, or clearly labeled on an extra sheet placed
underneath the top page of the test.
1) a) What is the gauge pressure at a
depth of 2 meters (6.5 feet) iin a storage tank of alcohol (density of the
alcohol is 0.82 gm/cc)?
in Nt/m²: 16,072 Nt/m2 in lb/in²: 2.34 lb/in2 in atmospheres: 0.159 atm.
b) If the tank contained water instead of
alcohol, what would the gauge pressure at the same depth be?
19,600 Nt/m2 .
2) a) If you apply a force of 3,000 lbs. on
a cylinder of area 25 in2, what is the gauge pressure on the fluid
behind the cylinder?
In lbs./in2 : 120 lbs/in2
In Nt/m2: 8.24 x 105
Nt/m2
b) If the fluid under the above pressure
pushes on another cylinder of area 0.12 in2, what will be the force
on this cylinder?
In lbs: 14.4 lbs.
In Nts: 64 Nts.
3) A small artery of inside DIAMETER 0.4 mm
and length 2.0 cm carries blood. Assume the beginning and the end of the artery
are at the same height.
a) If the pressure drop from the front to
the back of the artery is 1.6 mm Hg, what is the pressure drop expressed in Nt/m2
?
213 Nt/m2
b) Assuming there is the above pressure
drop, and given that the viscosity of the blood is 4 x 10-3 Pl
(about four times that of water), what is the volume flow of blood per time
through the artery (assume laminar flow) expressed:
in m3/sec: 1.67 x 10-9
m3/sec
in cc/sec: 0.00167 cc/sec
c) Given that the density of blood is 1.05
gm/cc, by how much would the blood pressure increase due to gravity by going
down a distance of 50 cm (from the heart to the knee)?
In Nt/m2: 5,145 Nt/m2
In mm of Hg: 38.7 mm of Hg.
4) a) Assume a house has 2,000 ft2
of floor (and ceiling) space (50 ft x 40 ft), all of it with 8 ft ceilings.
What is the volume of air space in this room?
in ft3 : 16,000 ft3;
in m3 : 453 m3
Now assume the temperature in the room is
set to be 76oF.
b) Calculate the number of moles of air in
this room:
18,530 moles
c) Is the number of moles of air in the room
when the temperature is 40oF [more, the same, or less] than when the
temperature is 76oF ?
more.
d) Given that the heat capacity of air (at
constant pressure) is (7/2)*R, how much energy would it take to heat up the air
in this room from 40°F to 76°F ?
1.076 x 107 Joules = 2.99
kW-hr
e) At $.08 / kW-hr, what would this energy
cost?
$0.239 = 23.9 cents
f) If the air in this house is replace by
outside air at the rate of once every 3 hours, how much would it cost to keep
this room heated for one month assuming the outside temperature and inside
temperature remained constant during the whole month and assuming the outgoing
hot air did not warm up the incoming cold air?
(Neglect other sources of heat such as warm bodies and losses due to
radiation and conduction).
$57.42
5) A house with 2,000 ft2 of
floor (and ceiling) space has thermal insulation due to sheetrock and fiberglass
with a total value of R = 21 ft2*oF*hr/BTU. Assume the average inside temperature
is 76oF and the average
outside temperature is 40oF.
Ignore other sources of heat loss such as through the walls, through the
floor, via convection and radiation.
a)
What is the average heat loss per time (in Watts) due to conduction
through the ceiling?
1,005 Watts
b) If the cost of energy is $0.08 / kW*hr,
what will the cost be for a month to replace the energy lost by conduction?
$57.91
c)
If the inside temperature is reset to 68o, what will the new
average heat loss per time (in Watts) due to conduction through the ceiling be?
782 Watts.
6 a) How much energy does it take to heat up
355 cc's of water (12 fluid ounces) (1
cc = 1 milliliter = 1 gram) from 40oF to boiling (212oF)
?
142,000 Joules = 33,900 calories
b) How much energy does it take to boil 355
cc's of water (if the water is already at 212oF) ?
802,450 Joules = 191,700 calories
c) If a person burns energy at the rate of
225 Watts, how much cold water (at 40o) is needed each hour to keep
the person cool by evaporation (assume no heat is lost by conduction or
radiation ?
305 cc/hr.
7) Assume a certain person has an average
skin temperature of 95°F and a skin area of 1.27 m2.
a) How much energy does this person radiate
per second (in Watts)?
629 Watts
b) If the air temperature is -60°F, how much
heat energy per time does this person receive from the air due to radiation?
170 Watts
c) What is the net power lost or gained by radiation
by the person?
459 Watts.
8)
a) State the First Law of
Thermodynamics:
b) Where does this law
come from, that is, is it a re-statement of a previous law?
c) State the Second Law of
Thermodynamics
d) Where does this law come from?: