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Quiz #7
PHYSICS 101
Nov. 15, 2000
1) The input to a Venturi tube has a cross sectional area of 1.2x10-4 m2. The tube narrows down to a
quarter this area in the middle. Water enters the tube with a volume flow rate of Q=1.44x10-4 m3/s.
h1
h2
P1,v1
Flow
P2,v2
a)What is the velocity of the water in region 2 of the tube? If you do not know, assume a velocity
of 5 m/s. (2 pts)
b) What is the pressure at the top of tube 2? (1 pt)
c) What is the difference in pressure at the bottom of tubes 1 and 2. (2 pts)
(CONTINUED ON OTHER SIDE)
Rewrite and sign the honor pledge: “I pledge my honor that I have not violated the Honor
Code during this examination.”
_________________________________________________________________________
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2) A spherical aluminum ball of mass = 7.2x10-4 kg, radius = 0.004 m, volume=2.7x10-7 m3 is
dropped into a tube of glycerine filled to the 0 cm line, as shown in the drawing below (the ball is
not to scale). The viscosity of glycerine is 1.5 Pa s; its
density is 1260 kg/m3.
0 cm
10 cm
20 cm
a) Draw the free body diagram and give an expression for each of the forces. (2 pts)
b) Assume the ball reaches a terminal speed by the 10 cm mark. How long does it take the ball to
traverse the distance between the 10 cm and 20 cm lines? (3 pts)
Your name __________________________
Quiz #7
PHYSICS 101
Nov 14, 2001
1)A ball of radius 0.0004 m and density 2700 kg per cubic meter is dropped into a 4 meter deep
pond of water with viscosity 0.001 Pa s. Assuming that the ball reaches its maximum (terminal)
velocity immediately, how long does it take for it to get to the bottom of the pond from the surface?
You may ignore the buoyant force. (5 pts)
(CONTINUED ON OTHER SIDE)
Rewrite and sign the honor pledge: “I pledge my honor that I have not violated the Honor
Code during this examination.”
_________________________________________________________________________
_________________________________________________________________________
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2)Water enters the Venturi tube in the figure below from the left with a velocity of v1=0.5 m/s. The
cross sectional area of the tube near where h1 is measured is 0.0004 square meters. In the center of
the tube, the diameter is half that of the value at the left end.
h1
h2
P1,v1
Flow
P2,v2
a) What is the velocity of the water, v2, near h2? (2 pts)
b)What is the difference in heights, h1-h2, of the water in the columns? (3 pts)
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Quiz 7
Physics 101.
November 13, 2002
Useful number:
r=1000 kg/m3 for water
1 A tank of water drains from a tube of radius 3 mm as shown. The water leaves the
tube with a velocity v=10 m/s.
(a) What is the flow rate, Q, of water leaving the tube? [ 2 points]
(b) What is the distance H shown? [2 points]
p
H
h=2m
(c) What is the absolute pressure in the pipe at the point “p”, which is 2 m above the
bottom of the tube? [2 points]
(OVER)
2. A plastic ball of mass M=10 kg is submerged in a tank of water as shown. The ball
has a lower density than water. A scale is attached to the rope holding down the ball.
The scale measures a “weight” of M’=8 kg (i.e., the scale measures a force = M’g, with
M’=8 kg). What is the volume of the ball? [ 4 points]
scale
Rewrite and sign the honor pledge: “I pledge my honor that I have not violated the
Honor Code during this examination.”
Signature_________________________
Name__________________
Quiz 7
Physics 101.
November 12, 2003
Possibly useful numbers: Po=1.0x105 Pa. ρair= 1.3 kg/m3, ρwater= 1000 kg/m3
1. Air is blown through a tube that opens to the atmosphere with a velocity v=20 m/s.
A branch off this line sticks into an open bucket of water. The radius of the tube is
r=1.0 cm. Assume that the air behaves as a perfect fluid (i.e., has a constant
density).
v
fan
P0
P
h
a. What is the volume flow rate of air? [2 point]
b. What is the pressure P at the point shown. (Hint: P is the same as in the tube
with airflow. Also, out away from the exhaust, the velocity is zero.) [2 points].
c. What is the height, h? [2 points]
(OVER)
2. An aluminum sphere of radius R=1 m3 (ρAl=2700 kg/m3) has a hollow center. As a
result it is exactly neutral buoyant (i.e., neither sinks for rises to the surface) in
water. What is the radius, r, of the inner hollow portion? [4 points].
R
r
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Honor Code during this examination.”
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P2 v2
Flow
H
Q
P1
v1 R1
P3 v3 R3
Another
liquid
Water
PRINT YOUR NAME:
QUIZ 7
Throughout, please box your answers!
Physics 101, Fall 2005
Problem 1. A cylindrical candle floats in a measuring cup full of water with density 1
gm/cm3 . It is made of volume 100 cm3 of wax with density 0.2 gm/cm3 and has a lead pellet
of mass 5 gm and negligible volume embedded in its bottom which makes it float upright
and causes it to extinguish itself automatically.
Starting point
Water
End point
Water
Pellet
a. (2 pts) What volume of water does the candle displace before it is lit (fig./left)?
b. (2 pts) The candle burns without dripping into the water, so it reduces to a shorter length
by evaporating mass (wax) until the water reaches the wick when it is barely submerged .
What is the final volume of leftover candle (fig./right)?
c. (1 pts) Has the water level in the measuring cup gone up or down ? Justify your answer.
QUIZ 7
Physics 101
Problem 2. Blood Flow
(1) (2 pts) The mean (gauge) pressure in an artery near the heart is 13.3 kPa (Kilo-Pascal).
Your head is about 0.4 m above your heart. Neglecting the viscosity of blood and changes
in the cross-sectional areas of the arteries, calculate the mean (gauge) pressure in arteries
near your brain. (Assume that the density of blood is the same as that of water).
(2) (3 pts) The aorta has an inner radius of approximately 0.25 cm. The average speed of
blood through the aorta is 1 m/s. A capillary has an inner radius of approximately 0.005 mm
and the average speed of blood through a capillary is 1 cm/s. Assuming that all the blood
flowing through the aorta flows through the capillaries determine the number of capillaries
in the circulatory system.
Rewrite and sign the pledge: I pledge my honor that I have not violated the Honor Code during
this examination.
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