Physics 141, Midterm Exam #2

Tuesday
October 25, 2016

8.00
am Ð 9.30 am

**Do not turn the
pages of the exam until you are instructed to do so.**

**Exam rules:** You may use *only* a writing
instrument while taking this test.
You may *not* consult any
calculators, computers, books, nor each other.

1.
Answer the multiple-choice questions (problems 1
Ð 10) by marking your answer on the scantron form. For each multiple-choice question
(problems 1 Ð 10), select only one answer.
Questions with more than one answer selected will be considered
incorrect. **If your student ID is not listed properly on the Scantron form (in the
bubbles on the lower-left corner), the form will not be processed and you lose
points for all multiple-choice questions.**

2.
Problems 11, 12, and 13 must be answered in the
blue exam booklets **(answer questions 11
and 12 in booklet 1 and question 13 in booklet 2.)** The answers need to be well motivated
and expressed in terms of the variables used in the problem. You will receive partial credit where
appropriate, but only when we can read your solution. Answers that are not motivated will not
receive any credit, even if correct.

At the
end of the exam, you need to hand in your exam, the blue exam booklets, and the
scantron form. All items must be
clearly labeled with your name, your student ID number, and the day/time of
your recitation. **If any of these items are missing, we will
not grade your exam, and you will receive a score of 0 points.**

**You are required to complete the following Honor Pledge for Exams.
Copy and sign the pledge before starting your exam.**

ÒI affirm that I will not give or receive any unauthorized help on this exam, and that all work will be my own.Ó

_____________________________________________________________________________

_____________________________________________________________________________

_____________________________________________________________________________

Name: ______________________________________________________________________

Signature: ____________________________________________________________________

__INTENTIONALLY LEFT BLANK__

__Useful Relations:__

__Problem 1__ (2.5 points) SCANTRON
FORM

Look
at the images below. What do you see?

Landing in Beijing.

On the ground in Toronto.

1. Runway 36L in Tokyo.

2. A Boeing 737 from American Airlines.

3. Your instructorÕs favorite airplane from his favorite airline.

4. A major problem (look at the smoke).

5. Smog in Beijing.

6. None of the above

__Problem 2__ (2.5 points) SCANTRON
FORM

Which of the diagrams in the following figure corresponds to a system of one electron and one positron that start out far apart, moving straight toward each other with nonzero initial velocities?

1. (a)

2. (b)

3. (c)

4. (d)

5. (e)

6. (f)

__Problem 3__ (2.5 points) SCANTRON
FORM

A chain of metal links is coiled up in a tight ball on a low-friction table. You pull on a link at one end of the chain with a constant force. Eventually the chain straightens out to its full length and you keep pulling until you have pulled your end of the chain a total distance of 4.5 m. By what distance does the center of mass of the chain move?

1. 4.5 m.

2. 7.1 m.

3. 1.9 m.

4. 3.2 m.

5. 5.8 m.

__Problem 4__ (2.5 points) SCANTRON
FORM

The figure below shows the potential energy
distribution of a star-planet system.
Three different types of motion of the planet are represented by the
three energy states indicated (*A*, *B*,
and *C*). Which of these states represents the
planet in an elliptical orbit?

1. *A*.

2.
*B*.

3. *C*.

__Problem 5__ (2.5 points) SCANTRON
FORM

The
following figure shows a portion of a graph of energy vs. time for a mass on a
spring, subject to air resistance. Identify
the three curves as to what kind of energy each represents.

1.
*A* = Kinetic energy, *B* = Potential energy, *C* =
Total energy.

2.
*A* = Kinetic energy, *C* = Potential energy, *B* =
Total energy.

3.
*B* = Kinetic energy, *C* = Potential energy, *A* =
Total energy.

4.
*B* = Kinetic energy, *A* = Potential energy, *C* =
Total energy.

5.
*C* = Kinetic energy, *A* = Potential energy, *B* =
Total energy.

6.
*C* = Kinetic energy, *B* = Potential energy, *A* =
Total energy.

__Problem 6__ (2.5 points) SCANTRON
FORM

The following figure shows a graph of the potential energy vs interatomic distance for a particular molecule. The energy of all bound states are shown in the figure.

You heat a sample of molecules to such a temperature that all atoms are in one of the four bound states. All transitions between the states occur with equal probability. What is the energy of the photon that is emitted by this sample of molecules that has the largest wavelength?

1. 2.1 eV

2. 2.3 eV

3. 1.8 eV

4. 1.1 eV

5. 0.5 eV

6. 0.2 eV

7. 0.3 eV

8. 0.6 eV

9. 1.2 eV

10. 0.9 eV

__Problem 7__ (2.5 points) SCANTRON
FORM

The following figure shows the path of a comet orbiting a star.

At what location on the path has the comet its lowest kinetic energy?

1. A.

2. B.

3. C.

4. D.

5. E.

__Problem
8__ (2.5 points) SCANTRON
FORM

Which energy diagrams in the following figure are appropriate for the following situations?

a) Nuclear states.

b) Electronic states of a single atom.

c) Hadronic states.

1. (1=a), (2=b), (3=c).

2. (1=a), (2=c), (3=b).

3. (1=b), (2=a), (3=c).

4. (1=b), (2=c), (3=a).

5. (1=c), (2=a), (3=b).

6. (1=c), (2=b), (3=a).

__Problem
9__ (2.5 points) SCANTRON
FORM

Consider the energy diagram shown in the figure below. Match the description of a process with the corresponding arrow in the figure.

a) Absorption
of a photon whose energy is *E*_{1}
Ð *E*_{0}.

b) Absorption from an excited state (a rare event at low temperatures).

c)
Emission of a photon whose energy is *E*_{3} Ð *E*_{1}.

d) Emission
of a photon whose energy is *E*_{2}
Ð *E*_{0}.

1. (1=a), (2=b), (3=c), (4=d).

2. (1=a), (2=c), (3=b), (4=d).

3. (1=a), (2=d), (3=c), (4=b).

4. (1=a), (2=c), (3=d), (4=b).

5. (1=b), (2=a), (3=c), (4=d).

6. (1=c), (2=a), (3=b), (4=d).

7. (1=c), (2=d), (3=a), (4=b).

8. (1=d), (2=c), (3=a), (4=b).

9. (1=d), (2=b), (3=c), (4=a).

10. (1=d), (2=a), (3=b), (4=c).

__Problem
10__ (2.5 points) SCANTRON
FORM

A particle moves inside a circular glass tube
under the influence of a tangential force of constant magnitude *F*, as shown in the figure.

Can we associate a potential energy with this force?

1. Yes.

2. No.

3. Insufficient information available to answer this question.

__Problem 11__ (25 points) ANSWER
IN BOOK 1

Consider
and object consisting of two masses *M*
connected by a low-mass spring of spring constant *k _{s}*. When you
exert an upward force of 2

At one point, a larger constant force is applied (*F* > 2*Mg*) and the object starts moving up. At some later time, the stretch of the
spring has increased to *s _{f}*,
and the object is located as shown on the right in the figure.

a. At this time, what is the speed of the center of mass of the object?

b. At this time, what is the vibrational kinetic energy of the object?

Express all your answers in terms of the variables provided. Your answers must be well motivated.

__Problem 12__ (25 points) ANSWER
IN BOOK 1

A car of mass *M* is
rounding a horizontal circular curve of radius *R*. The coefficient of
static friction between the car tires in the road is *m*_{s}.

a. What is the maximum speed with which the car can go around the curve?

You drive the same car of mass *M* with speed *v,* trying to
go around a circular banked curve of radius *R*
and bank angle *q*.
You discover that the road is iced over and there is no friction between
your tires and the road.

b. If you want to go around the curve, what must be your speed?

c. What happens if your speed is below the speed you calculated in b)?

Express all your answers in terms of the variables provided. Your answers must be well motivated.

__Problem 13__ (25 points) ANSWER
IN BOOK 2

The Stanford Linear Accelerator Center (SLAC), located at
Stanford University in Palo Alto, California, accelerates electrons through a
vacuum tube of length *L*.

Electrons of mass *m*,
which are initially at rest, are subjected to a continuous force *F* along the entire length of the tube
and reach speeds very close to the speed of light

a. Calculate the final energy of the electrons.

b. Calculate the final momentum of the electrons.

c. Calculate the final speed of the electrons.

d. Calculate
the time required to travel the distance*
L*.

Express all your answers in terms of the variables provided. Your answers must be well motivated

__INTENTIONALLY LEFT BLANK__

__INTENTIONALLY LEFT BLANK__

__INTENTIONALLY LEFT BLANK__

__INTENTIONALLY LEFT BLANK__

__INTENTIONALLY LEFT BLANK__