Lecture 10, 9 27 11rads.physics.miami.edu/optics/ken/CLASS101_F_11_old... · 2012-03-23 · 9/27/11...
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9/27/11 1 Physics 101 Tuesday 9/27/11 Class 10 Chapter 6.5 – 7.2 Circular motion Work done by a constant Force Kinetic Energy and work-energy theorem Questions Did you read the assignment and study the example problems before class today? A) yes, and I have done this every time B) Yes, but this is an exception C) no, but this is an exception D) No, I don’t bother, I wait until after the class Questions I spent _____ hours studying for the last test A) < 1hr B) between 1 hr and 3 hrs C) between 3 hrs and 10 hrs D) more than 10 hrs questions To study for the exam I A) reread the chapter B) did the example problems in the book C) did many of the suggested problems D) read many of the suggested problems E) looked through the suggested problems, clicker questions, discussion session questions, in class worked examples.
Transcript of Lecture 10, 9 27 11rads.physics.miami.edu/optics/ken/CLASS101_F_11_old... · 2012-03-23 · 9/27/11...
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Physics 101 Tuesday 9/27/11 Class 10"
Chapter 6.5 – 7.2"Circular motion"Work done by a constant Force"Kinetic Energy and work-energy theorem"
Questions!
Did you read the assignment and study the example problems before class today? A) yes, and I have done this every time B) Yes, but this is an exception C) no, but this is an exception D) No, I don’t bother, I wait until after the class
Questions!
I spent _____ hours studying for the last test A) < 1hr B) between 1 hr and 3 hrs C) between 3 hrs and 10 hrs D) more than 10 hrs
questions!
To study for the exam I A) reread the chapter B) did the example problems in the book C) did many of the suggested problems D) read many of the suggested problems E) looked through the suggested problems, clicker questions, discussion session questions, in class worked examples.
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Ques%on 6.11 Missing Link
A Ping-‐Pong ball is shot into a circular tube
that is lying flat
(horizontal) on a
tabletop. When the
Ping-‐Pong ball leaves
the track, which path will it follow?
a b c
d e
Reading Quiz!
Circular motion!
You are a passenger in a car, not wearing a seat belt. The car makes a sharp leD turn. From your perspecFve in the car, what do you feel is happening to you?
a) you are thrown to the right
b) you feel no particular change
c) you are thrown to the left
d) you are thrown to the ceiling
e) you are thrown to the floor
Around the Curve I
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a) centrifugal force is pushing you into the door
b) the door is exerting a leftward force on you
c) both of the above
d) neither of the above
During that sharp leD turn, you found yourself hiIng the passenger door. What is the correct descripFon of what is actually happening?
Ques%on 6.10b Around the Curve II Circular motion!
© University of Colorado, Boulder, 2004
A car rounds a banked curve at some speed without skidding. The radius of curvature of the curve is R. A possible free-body diagram (which may or may not be correct) is shown.
\
a
mg
f(fric)
N
What can you say about ffric, the magnitude of the force of friction? A: ffric= µS N B: ffric= µKN C: Neither.
Circular motion!© University of Colorado, Boulder, 2004
A car rounds a banked curve at some speed without skidding. The radius of curvature of the curve is R. A possible free-body diagram (which may or may not be correct) is shown.
\
a
mg
f(fric)
N
What can you say about the direction of ffric? A: It is in the direction shown in the free-body diagram. B: It is in the direction opposite shown in the diagram. C: The direction depends on the speed of the car.
Circular motion!
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Circular motion!
A person sits normally in a chair on a ferris wheel, which rotates with constant speed. As they go around the circle, at which point is the magnitude of the net force on the person a MAXIMUM?
A: Top B: Bottom C: Right D: Same at all positions.
Circular motion!
A person sits normally in a chair on a ferris wheel, which rotates with constant speed. At which point is the magnitude of the normal force of the seat on the person a MAXIMUM?
A: Top B: Bottom C: Right D: Same at all positions.
Circular Motion!
A bucket of water is swung in a circle at constant speed in a vertical plane as shown. The bucket is swung fast enough that the water does not spill out.
The net force on the water as it is swung has maximum magnitude at... A: Top. B: Bottom. C: Right D: (Same at all positions.)
N R
B
T
Circular motion!
A bucket of water is swung in a circle at constant speed in a vertical plane as shown. The bucket is swung fast enough that the water does not spill out.
Consider the normal force exerted on the water by the bucket when the bucket is at the three positions shown: R, T, B. The magnitude of the normal force is a minimum at A: Top. B: Bottom. C: Right
D: (Same at all positions.)
N R
B
T
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Circular motion!
A bucket of water is swung in a circle at constant speed in a vertical plane as shown. The bucket is swung fast enough that the water does not spill out.
The speed the bucket must have to prevent water spilling out is:
A: gr
B: mgr
C: mg / r The bucket is 4.0 kg, the radius is 1.0 m (does this matter?).
N R
B
T
Work!
Albert Einstein lowers a book of mass m downward a distance h at constant speed v. The work done by the force of gravity is... A: + B: - C: 0
Work!
Albert Einstein lowers a book of mass m downward a distance h at constant speed v. The work done by the force of Albert's hand is... A: + B: - C: 0
Work!
Albert Einstein lowers a book of mass m downward a distance h at constant speed v. The work done by the net force on the book is... A: + B: - C: 0
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Work! Work!
Work!
You push a beer keg up a (frictionless) ramp with constant speed. Suppose you push parallel to the ramp, with force "F".
The ramp travels a distance d along the ramp, ending at height h as shown.
How much work did YOU do on the keg? A) F d B) F d cos! C) zero D) F h (which is equal to F d sin!) E) None of these
Work!
You push a beer keg up a (frictionless) ramp with constant speed. Suppose you push parallel to the ramp, with force "F".
The ramp travels a distance d along the ramp, ending at height h as shown.
How much work did GRAVITY do on the keg? A) +mg d B) +mg d cos! C) zero D) +mg h (which is equal to +mg d sin!) E) None of these
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Work!
You push a beer keg up a (frictionless) ramp with constant speed. Suppose you push parallel to the ramp, with force "F".
The ramp travels a distance d along the ramp, ending at height h as shown.
What is the NET WORK done on the keg? A) zero B) positive C) negative D) Not enough information given.
Kinetic Energy!
By what factor does the kinetic energy of a car change when it’s speed is tripled? A) no change at al B) factor of 3 C) factor of 6 D) factor of 9 E) factor of 12
Kinetic Energy!
Car #1 has twice the mass of car #2, but they have the same kinetic energy. How do their speeds compare? A) 2 v1 = v2
B) v1 = v2
C) 4 v1 = v2
D) v1 = v2
E 8v1 = v2
2
Kinetic Energy!
Is it possible for an object to have a negative Kinetic Energy? A) Yes B) No
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Two stones, one twice
the mass of the other, are
dropped from a cliff.
Just before hitting the
ground, what is the final
speed of the heavy stone
compared to the light
one?
a) quarter as much
b) half as much
c) the same
d) twice as much
e) four times as much
Free Fall Free Fall
a) quarter as much
b) half as much
c) the same
d) twice as much
e) four times as much
Two stones, one twice
the mass of the other,
are dropped from a
cliff. Just before
hitting the ground,
what is the kinetic
energy of the heavy
stone compared to
the light one?
Reading Assignment!
Thursday 9/29 7.3 – 8.2 Tuesday 10/4 8.3 – 8.5
