Physics 201: Lecture 29 Review

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Physics 201 Lecture 29Review

• Final, Wednesday, 20 December 2005, PM.
• The 2 hour exam will have 25 questions,
• The exam will cover chapters 1 - 15
• Exam will be held in B10 Ingraham
• http//tycho.physics.wisc.edu/courses/phys201/fall
  06/Exams.html

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• 1) The pressure on the roof of a tall building is
  0.985 x 105 Pa and the pressure on the ground is
  1.000 x 105 Pa. The density of air is 1.29 kg/m3.
  What is the height of the building?
• A. 100 m
• B. 118 m
• C. 135 m
• 114 m
• None of the above

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Preflight 1
A venturi tube may be used as the inlet to an
automobile carburetor. If the 2.0-cm diameter
pipe narrows to a 1.0-cm diameter, what is the
pressure drop in the constricted section for an
airflow of 3.0 m/s in the 2.0-cm section? (fuel
density 1.2 kg/m3.)?      70 Pa      85
Pa      100 Pa     115 Pa      81 Pa
What is the concept that applies to this
situation? Pouissiuelles Law Pascals
principle Archimedes principle Bernoullis
principle
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Bernoullis Equation

• Pressure drops in a rapidly moving fluid
• whether or not the fluid is confined to a tube
• For incompressible, frictionless fluid

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Preflight 1
A venturi tube may be used as the inlet to an
automobile carburetor. If the 2.0-cm diameter
pipe narrows to a 1.0-cm diameter, what is the
pressure drop in the constricted section for an
airflow of 3.0 m/s in the 2.0-cm section? (fuel
density 1.2 kg/m3.)?      70 Pa      85
Pa      100 Pa     115 Pa      81 Pa
What can I use to extract quantities needed to
use the Bernoulli equation? Density is
constant Velocity of fluid is
constant Viscosity is negligible Volume flow
rate is constant
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Fluid Flow
Fluid flow without friction

• Volume flow rate ?V/?t A ?d/?t Av (m3/s)
• Continuity A1 v1 A2 v2
• i.e., flow rate the same everywhere
• e.g., flow of river

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Preflight 1
A venturi tube may be used as the inlet to an
automobile carburetor. If the 2.0-cm diameter
pipe narrows to a 1.0-cm diameter, what is the
pressure drop in the constricted section for an
airflow of 3.0 m/s in the 2.0-cm section? (fuel
density 1.2 kg/m3.)?      70 Pa      85
Pa      100 Pa     115 Pa      81 Pa
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• 2) Firemen connect a hose (8 cm in diameter) to a
  fire hydrant. When the nozzle is open, the
  pressure in the hose is 2.35 atm. (1 atm. 105
  Pa). The firemen hold the nozzle at the same
  height of the hydrant and at 45o to the
  horizontal. The stream of water just barely
  reaches a window 10 m above them. The diameter of
  the nozzle is about
• A. 8 cm
• B. 6 cm
• C. 4 cm
• 2 cm
• None of the above

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4. Wind at speed v is incident horizontally on a
windmill with rotors of radius r. The maximum
power that can be generated from the wind energy
is
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• 5) A large hydro-electric station can produce
  1000 MW power. Assuming that windmills are able
  to convert only 10 of the total energy incident,
  how many windmills with rotor area 200 m2 each
  are needed to harness the wind (?1 kg/m3) which
  is blowing at 10 m/s to achieve power output
  equal to 1000 MW?
• A. 103
• B. 104
• C. 105
• 106
• 107

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Preflight 2
A wind with velocity 10 m/s is blowing through a
wind generator with blade radius 5.0 meters. What
is the maximum power output if 30 of the winds
energy can be extracted? (air density 1.25
kg/m3.)      7.2 kW      14.7 kW      21.3
kW     29.4 kW     39.6 kW
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Preflight 3
The water level in identical bowls, A and B, is
exactly the same. A contains only water B
contains ice as well as water. When we weigh the
bowls, we find that      WA lt WB      WA WB
      WA gt WB      WA lt WB if the volume of
the ice cubes is greater than one-ninths the
volume of the water.     WA lt WB if the volume
of the ice cubes is greater than one-ninths the
volume of the water.
Eureka! Archimedes Principle. Weight of the water
displaced Bouyant Force
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• 1) A block of aluminum (density 3041 kg/m3) is
  lifted very slowly but at constant speed from the
  bottom of a tank filled with water. If it is a
  cube 20 cm on each side, the tension in the cord
  is
• A. 160 N
• B. 4 N
• C. 80 N
• 8 N
• None of the above

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Preflight 4
The amplitude of a system moving with simple
harmonic motion is doubled. The total energy will
then be      4 times larger      2 times
larger the same as it was half as
much     quarter as much
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Preflight 5
A glider of mass m is attached to springs on both
ends, which are attached to the ends of a
frictionless track. The glider moved by 0.2 m to
the right, and let go to oscillate. If m 2 kg,
and spring constants are k1 800 N/m and k2
500 N/m, the frequency of oscillation (in Hz) is
approximately      6 Hz      2 Hz 4 Hz 8
Hz     10 Hz
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Problem

• At t0, a 795-g mass at rest on the end of a
  horizontal spring (k127 N/m) is struck by a
  hammer, giving it an initial speed of 2.76 m/s.
• What is period of the motion?
• What is the frequency of the motion?
• What is the maximum acceleration?
• What is the total energy?

0.497 s
2.01 Hz
34.9 m/s2
3.03 J
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Problem

• A 810-g block oscillates on the end of a spring
  whose force constant is 60 N/m. The mass moves in
  a fluid which offers a resistive force
  proportional to its speed the proportionality
  constant is 0.162 N.s/m.
• Write the equation of motion and solution.
• What is the period of motion?
• What is the fractional decrease in amplitude per
  cycle?
• Write the displacement as a function of time if
  at t 0, x 0 and at t 1 s, x 0.120 m.

0.730 s
0.070