homework 15 – MOHAJER, CHRISTOPHER – Due: May 6 2008, 4:00 am
1
Question 1, chap 18, sect 2.
part 1 of 1
10 points
A cowboy at a dude ranch fills a horse
trough that is 1
.
6 m long, 64 cm wide, and
47 cm deep. He uses a 2
.
1 cm diameter hose
from which water emerges at 1
.
1 m
/
s .
How long does it take him to fill the trough?
Answer in units of min.
Question 2, chap 18, sect 2.
part 1 of 2
10 points
Calculate the mass flow rate of blood (of
density 1 g
/
cm
3
) in an aorta with a cross
sectional area of 2 cm
2
if the flow speed is
40 cm
/
s.
Answer in units of g
/
s.
Question 3, chap 18, sect 2.
part 2 of 2
10 points
Assume that the aorta branches to form a
large number of capillaries with a combined
crosssectional area of 2900 cm
2
.
What is the flow speed in the capillaries?
Answer in units of mm
/
s.
Question 4, chap 18, sect 2.
part 1 of 1
10 points
A 4 meter long hose of 2 cm diameter is
connected to a faucet, and a 3 meter long
hose, which has a diameter of 4 cm diameter,
is connected to the end of the first hose. At
the open end of the second hose water flows
out at a rate of 2.5 liters/minute. The open
end of the second hose is 2 meters higher than
the faucet. What is the ratio of the speed of
the water in the second hose to the speed of
the water flowing in the first hose?
1.
4
2.
1/4
3.
1/2
4.
2
5.
8
6.
1/8
7.
3/2
8.
1
Question 5, chap 18, sect 3.
part 1 of 2
10 points
You blow up an ordinary party balloon with
air until it has a diameter of 8 inches.
Your
friend blows up another balloon with helium
gas until it has a diameter of 12
.
5 inches. Air
consists mostly of O
2
and N
2
molecules, while
helium gas consists of He atoms. Assume the
pressure in each balloon is the same.
Compare the number of helium atoms to
the total number of O
2
and N
2
molecules.
Question 6, chap 18, sect 3.
part 2 of 2
10 points
Air is about 80% nitrogen and 20% oxy
gen.
Compare the weights of the two bal
loons.
(
Hint:
Imagine that there are 80 he
lium atoms in the helium balloon. Calculate
the mass, in atomic mass units, of this amount
of helium, and then compare to the mass of
the corresponding number of oxygen and ni
trogen molecules.)
Question 7, chap 18, sect 3.
part 1 of 2
10 points
A medic applies a force of 95 N to a 0
.
03 m
2
area that is bleeding.
What is the pressure in pascals that she
applies?
Answer in units of Pa.
Question 8, chap 18, sect 3.
part 2 of 2
10 points
What is the pressure in pounds per square
inch?
Answer in units of lb
/
in
2
.
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homework 15 – MOHAJER, CHRISTOPHER – Due: May 6 2008, 4:00 am
2
Question 9, chap 18, sect 3.
part 1 of 2
10 points
In a 99 s interval, 898 hailstones strike a
glass window of area 1
.
101 m
2
at an angle 29
◦
to the window surface. Each hailstone has a
mass 2 g and a speed 8
.
3 m
/
s.
If the collisions are elastic, find the average
force on the window.
Answer in units of N.
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 Spring '09
 KLEINMAN
 Physics, Work, Pressure measurement, CHRISTOPHER –

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