Name ________________________________________________________________________
Exam #3
Physics I
Fall 2003
If you would like to get credit for having taken this exam, we need
your name (printed clearly) at the top and section number below.
Section #
_____ 1
_____ 2
_____ 3
_____ 5
_____ 6
_____ 7
_____ 8
_____ 10
M/R 8-10 (Bedrosian)
M/R 10-12 (Bedrosian)
M/R 12-2 (Bedrosian)
T/F 10-12 (Washington)
T/F 12-2 (Hayes)
T/F 2-4 (Hayes)
M/R 2-4 (Schroeder)
M/R 12-2 (Shannon)
Questions
Part A
Value
32
Part B
24
C-1
20
C-2
24
Total
100
Score
If we catch you cheating on this exam,
you will be given an F in the course.
Sharing information about this exam with people who have not yet
taken it is cheating on the exam for both parties involved.
The Formula Sheets are the last two pages. Detach carefully for easier reference if you wish.
1
Name ________________________________________________________________________
On this exam, please neglect any relativistic and/or quantum mechanical effects. If you don’t
know what those are, don’t worry, we are neglecting them! On all multiple-choice questions,
choose the best answer(s) in the context of what we have learned in Physics I.
On calculation questions, show all work to receive credit.
Part A – Multiple Choice – 32 Points Total (8 at 4 Points Each)
Write your choice on the line to the left of the question number.
______ 1.
Select ALL of the following statements that we can conclude from Newton’s
Theory of Gravity. (Put all letters you choose to the left of the question number.)
A)
B)
C)
D)
______ 2.
Gravity works the same way everywhere in the universe and at all times.
The property of matter that relates force and acceleration also causes gravity.
The force of gravity obeys Newton’s Third Law.
The force of gravity is a conservative force.
In the figure, an electron e travels through a small hole in plate A and then toward
plate B. A uniform electric field between the plates slows the electron without
deflecting it. The direction of the electric field between the plates is:
Y
______ 3.
A) +X
B) –X
C) +Y
D) –Y
X
The figure below shows the path of a charged particle that passes through two
regions containing uniform magnetic fields of magnitudes B1 and B2. Its path in
each region is a half-circle. The fields are directed either into the page or out of the
page. The only force on the particle is due to the respective magnetic fields.
Select ALL of the statements below that we can correctly conclude:
A) The speed of the particle is constant.
B) The magnetic fields in the two regions are in opposite directions.
C) B1 > B2.
D) If we doubled B1, B2 and the initial velocity, the path would be the same.
2
Name ________________________________________________________________________
______ 4.
A uniform, constant magnetic field is directed into the page. A charged particle,
moving in the plane of the page, follows a counter-clockwise spiral of increasing
radius as shown. Select ALL of the choices below that we can correctly conclude:
A)
B)
C)
D)
______ 5.
The charge of the particle is positive.
The particle is speeding up.
The magnetic force does no work on the particle.
There must be another force on the particle in addition to the magnetic force.
Two point charges are arranged as shown. In which region(s) is there a point on the
line (not at infinity) where the net electric field due to the two charges is zero?
B) Region II only.
D) More than one of the regions.
A) Region I only.
C) Region III only.
______ 6.
A charged particle is moving in a circle at a constant speed in a magnetic field. The
period of the particle’s motion is independent of
A) the particle’s speed.
B) the particle’s charge.
C) the particle’s mass.
D) the magnetic field.
______ 7.
An electron moves from a point of lower electric potential to a point of higher
electric potential. Which one statement below is correct?
A) The electric force did positive work on the electron.
B) The electric force did negative work on the electron.
C) The electric force did no work on the electron.
D) There is not enough information to decide which of A-C above is true.
______ 8.
What are correct units for the electric field? Select ALL that apply.
A) N/C
B) J/C
C) T/m
D) V/m
3
Name ________________________________________________________________________
Part B – Graphing – 24 Points Total
A proton and an electron move (separately) in one dimension through a region with an electric
potential as shown below. The only force experienced by the two particles is due to the electric
field. The electron and proton are far enough apart so they do not interact with each other. Both
the electron and the proton start at d = 0 with K.E. (kinetic energy) = 3.2 x 10-17 J. Plot K.E. for
both particles versus distance from d = 0 to d = 100 cm. Show all work. Include the following:
1. Shape of the curve(s).
2. Minimum and maximum points.
3. Clearly labeled axes.
Potential (V)
100
0
d (cm)
20
40
60
80
100
Proton
KE (J)
0
d (cm)
20
40
60
80
100
Electron
KE (J)
0
d (cm)
20
40
60
80
100
4
Name ________________________________________________________________________
Part C – Problems – 44 Points Total
C-1 (20 points)
An unknown charged particle is accelerated from rest in an electric field. The potential
difference is –1.000 x 105 Volts. (From this we infer that its charge is positive.) It is observed in
a bubble chamber to travel in a circular path with a radius of 3.066 cm. The magnetic field in the
chamber is 0.500 T at a right angle to the particle’s path. What is the ratio of its charge to mass?
charge / mass: _________________________________ units C / kg
5
Name ________________________________________________________________________
C-2 (24 points)
Calculate the electric field and electric potential at point A (“X marks the spot”). Assume the
electric potential is zero at infinity. The only charges are +e (one proton) and –e (one electron).
Y
A
6.0 x 10–11 m
X
+e
-e
6.0 x 10–11 m
Point A:
E field X Component: ___________________ units ________
E field Y Component: ___________________ units ________
Electric Potential:
___________________ units ________
6
Name ________________________________________________________________________
Formula Sheet for Homework and Exams – Page 1 of 2
1.
v  v 0  a t  t 0 
21.
2.
x  x 0  v 0 ( t  t 0 )  12 a ( t  t 0 ) 2
K  12 m v 2  12 m (v x  v y )
22.
3.
x  x 0  12 ( v0  v)( t  t 0 )
23.
K f  K i  Wnet


U    Fcons  dx
4.
x  x 0  v( t  t 0 )  12 a ( t  t 0 ) 2
24.
U g  m g (y  y 0 )
25.
U s  12 k ( x  x 0 ) 2
26.
27.
28.
 K   U  Wnoncons
s  r
v tangential   r
a tangential   r
2
2
6.
v 2  v 02  2a x  x 0 
 

 F  Fnet  m a
7.
T
8.
a centripetal 
29.
30.
  0  t  t 0 
Fcentripetal


p  mv

 
dp
 F  Fnet  d t



J   Fnet dt   p


P   pi


dP
  Fext
dt
31.
   0  0 ( t  t 0 )  12 ( t  t 0 ) 2
32.
   0  12 (0  )( t  t 0 )
33.
   0  ( t  t 0 )  12 ( t  t 0 ) 2
M   mi
38.
5.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
2r
v
v2
 2 r
r
v2
m
 m 2 r
r
35.
 2  02  2   0 
   
a  b  a b sin( )
36.
I   m i ri
34.
37.
39.
1
1
x cm   m i x i y cm   m i y i
M
M


P  M v cm
   
a  b  a b cos()  a x b x  a y b y
 
W  Fd
 
W   F  dx
40.
41.
42.
43.
44x. m1 v1, x ,before  m 2 v 2, x ,before  m1 v1, x ,after  m 2 v 2, x ,after
44y. m1 v1, y ,before  m 2 v 2, y ,before  m1 v1, y ,after  m 2 v 2, y,after
m1  m 2
2 m2
v1,i 
v 2 ,i
m1  m 2
m1  m 2
2 m1
m  m1

v1,i  2
v 2 ,i
m1  m 2
m1  m 2
45a. v1,f 
45b. v 2,f
7
2
K rot  12 I  2
 
W     d
  
  r F

 dL

  I  d t
  
l  r p


L  l i


L  I
Name ________________________________________________________________________
Formula Sheet for Homework and Exams – Page 2 of 2

m m
46a. | F |  G 1 2 2
r

m m
46b. F  G 1 2 2 r̂
r

1 | q1 || q 2 |
47a. | F | 
4  0
r2

1 q1 q 2
47b. F 
(r̂ )
4  0 r 2

1 | qi |
48a. | E i | 
4   0 ri 2

1 qi
(r̂i )
48b. E  
4   0 ri 2


49. F  q E
50.
51.
52.
1 qi
4   0 ri
U  qV
 
V    E  dx
V
V
x
V
53y. E y  
y

 
54. F  q v  B
mv
55. r 
qB
53x. E x  
Useful Constants
(You can use the approximate values on tests.)
Universal Gravitation Constant
G  6.67310 11 N m 2 kg 2  6.67 10 11
Electrostatic Force Constant
1
 8.987551788 10 9 N m 2 C  2  9.0 10 9
4  0
Magnetic Constant
 0  4  10 7 H m 1  1.26 10 6
Speed of Light in Vacuum
c  2.99792458 10 8 m s 1  3.010 8
Charge of a Proton
e  1.602176462 10 19 C  1.6 10 19
Electron-Volt Conversion Constant
1eV  1.602176462 10 19 J  1.6 10 19
Mass of a Proton
m p  1.6726215810 27 kg  1.67 10 27
Mass of an Electron
m e  9.10938188 10 31 kg  9.110 31
8