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PHYSICS221
FALL 2OO4
EXAM 3
Name (printed):
ID Number:
SectionNumber:
Recitation Instructor:
INSTRUCTIONS:
i.
Put away all materials except for pens, pencils, erasers and your calculator.
ii.
This is a 90 minute exam and contains 25 multiple choiceproblems.
All problems are worth 3 points each.
iii.
In marking the multiple choicebubble sheetuse a number 2 pencil. Do NOT use
ink. If you did not bring a pencil, ask for one. Fill in the appropriate circles
completely. If you need to change any entry, you must completely eraseyour
previous entry. Also, circle your answers on this exam.
iv.
Carefully read each problem and its five possible answers before beginning to work
the problem. Selectone and only one answer for each problem. Choosethe answer
that is closestto the correct one.
v.
Pleaseturn over or cover your bubble sheetwhen you are not marking it.
vi.
Before handing in your exam, be sure that your answerson your bubble sheetare
what you intend them to be. If you want to, copy down your answers on a piece of
unused scratch paper for comparison with the answer key to be posted later.
vii.
When you are finished with the exam, place all exam materials, including the bubble
sheet,the exam itself, and scratch paper that you used for the exam, in your folder
and return the folder to your recitation instructor.
viii.
No cell phone calls allowed. Either turn off your cell phone or leave it at home.
Anyone taking cell phone calls (must leave the testing room) will not be allowed to
return.
GOOD LUCK!!
PHYSICS22I
EXAM 3
FALL 2OO4
55.
a,_
Two insulatingsheetshavechargeQr. andQn uniformly
distributedthroughouttheir volumes.PointA is half-way
betweenthe two sheets.For which valuesof Ql andQn
{
will E at point A havethe largestmagnitude?
Qq
:
,,3\Qr + q
(}PL:*e
Qn:+9
Qn:-g
C) Ql:+2q
Q n= + 2 q
D) AnswersA andB areequalandlargerthananswerC.
E) AnswersA andC areequalandlargerthananswerB.
56.
Which of the following graphsbestrepresents
the lS(rll for a charged,conductingsphere
with radiusR?
E
t
\
\
1
\
t\
t
'
t
\
\
\
\
57.
A boardis suppportedby two triangularcross
sectionstandsasshown. Everythingis at rest.
The net torqueD"i is evaluatedfour times:
aboutpoint l, point 2, point 3 andpoint4.
Which of the followineis correct?
'*3
1
,t--
A) The net torqueaboutpoint I is the largest.
B) The net torqueaboutpoint 3 is the largest.
C) The net torqueaboutpoint 3 is largerthanthe net torqueaboutpoints2 and4 but
smallerthanthe nettorqueaboutpoint l.
_D) The net torqueaboutpoint 2 andthe net torqueaboutpoint 4 arethe smallest.
net torqueaboutiach point is the same.
@the
Two point chargesarelocatedon thex-a,xis.gr is at x : 0 andgz is locatedat
x : 2. If E = 0 for somegiven0< x'<2 thenwhichof the followingis true?
58.
j
(
Yl
gr andQ2musthaveoppositesigns.
Dqt md qz musthavethe samesign.
lq,ltruttoequal
lezl
D) Both A andC.
E) Both B andC.
A + 4 nC point chargeis separatedby somedistancefrom an + 8 nC point charge. If
the force experiencedbythe +4 nC chargeis F:0.1 N? - 0.2 NJ, what is the force
experiencedby the +8 nC charge?
59.
,
f
Ly-
l
A
0.1\i +0.2Nj
B)+0.lNi-0.2Nj
c) * 0.2N?+ 0.4Nj
D) + 0.2N?- 0.4NJ
E) + 0.2Ni + 0.4Nj
60.
A stick restson a horizontalfrictionlesstable.A puck with initial speedve hits the stick
at oneend.Which of the following quantitiesis conservedin this collision?(p : total
linearmomenfum,L: total angularmomenfum,KE : total kinetic energy)
A) L only
B) p only
C) p andKE only
andKE only
-AL
lyb
61.
andL only
A personhasjust arrangeda 5.0-mlong,uniform,boardof massl0 kg sothatit rests
atoptwo wedgesplacedunderthe left endand2.0 m from the right end,asshownin the
figure below.A 3.0-kgsmallbox (pointmass)is placedon the right endof the board.
Find the magnitudeof the normalforceexertedby the left wedgeon the boardjust after
the box hasbeenplaced.
A) 77N
B) 64N
c) 5lN
D 3.3N
Gilo.oN
\*-/
The figure below is the position vs time graph of a particle in simple harmonic motion.
\
tl
C)
L
Cg
C'
u)
I\
I t
I \
I t
I
I
\
I I
I
x
\.
-
t I
I
62.
I
t I
\
I
/ (l square: I s )
t I
I
I
Theamplitudeof the motionis:
A) 2m
@o*
C) 6m
D) 8m
E) lOm
Theperiodof the motionis:
63.
/-(
A) 2s
(E+s
C) 5s
D) 7s
E) 13s
64.
The x(t) functioncanbe written asx(t) : A cos(at+il. Determinethe phaseangleQ.
A)
---^
-71
(-p)-nt2
c)0
D) +r/2
E) +r
A positivepoint chargeis broughtneara neutralmetalslab,without touchingit. Both the
point chargeandthe slabaresurrounded
by vacuum(a perfectinsulator).What is the
resultingelectrostaticforcebetweenthe two objects?
65.
F,\
I
\
due to the induced chargeseparationin the metal slab.
\A)ettraction,
B) Attraction, due to the net negative chargeinduced in the metal slab.
C) Repulsion, due to the induced chargeseparationin the metal slab.
D) Repulsion, due to the net positive chargeinduced in the metal slab.
E) There is no electrostaticforce betweenthem.
66.
An electron moving in the +x direction entersa region with a uniform electric field
E = Eo j. Choosethe option that best describesthe trajectoryof the electron.
Eoj
electron o{:::
,...IL
C
tta
v+
I
l----+
67.
r
A dipole is placed in a uniform electric field as shown in the figure. Which of the
following statementsis true?
net forceon the dipoleis zeroandthe nettorqueis zero.
)\The
qpy'The net forceon the dipoleis zeroandthe nettorqueproducesa clockwiserotation.
C) The net forceon the dipoleis to the right andthe net torqueis zero.
D) The dipoleis in stableequilibrium.
E) The dipole is in unstableequilibrium.
The figtre belowrepresents
the orbit of a cometaroundthe sun.[n which of the indicated
pointsis the speedof the cometgreatest?
68.
Comet
A
( n)xtpoint I.
Yl AtpointII.
C) At point III.
D) At point IV.
E) The speedis the sameat all pointsin the orbit.
A light weightrotor (ignoreits mass)hastwo point-like 100g massesthat canbe in two
positions.
69.
lQ<,w\
<.-)
!C)
<an
tos
its verticaloris with a periodof I .0s,what is the rotor's
If at t : 0 the rotor spins.about
=
periodat t l0s, afterthe masseshaveslid out to their newpositions?
,r4a
L4) 4.0s
B) 2.0s
C) 1.0s
D) 0.50s
E) 0.25s
70.
A workerusesa light thin rod (teat asmassless)
to pick up a 5.00kg mass. Theworker'sright hand
is at the far endof the rod, the worker'sleft handis
0.600m from his right handandthe 5.00kg masscan
be approximatedasa point masslocated2.00m from
the worker'sright hand. Whatmagnitudeof forcemust
the worker'sleft handprovideto maintainthe rod and
massin the horizontalconfigtrationshown?
A) 49.0N
B) 9 8 . 0N
c)
71.
il4N
1 4 7N
1 6 3N
A2.0 kg massattached
to a massless
springoscillatesbetween*.25 cm on a frictionless
horizontaltrack. If at x:0 themasshasa speedof 3.0 m/s,whatis theperiodof the
oscillation?
A) 8.3 x l0-2s
rej 5.2x lo-rs
>C r.2x lors
D) 1.4x 102s
E) 2.9 x 102s
72.
A massis launcheddirectlyupwardalongthe radialdirectionfrom the earth'ssurface
with an initial speedof l0 km/s. Whatwill the mass'sspeedbe whenit is 2000km from
the earth'ssurface?
A) 2.23km/s
B) 4.46km/s
6.19km/s
A
( D) 8.38km/s
tt.zlcmls
E
73.
A satelliteis in a circularorbit 1000km aboveearth'ssurface.What is the magnitudeof
its velocity?
fo)t.rs x lo'm/s
Bt 7.90x lo3m/s
C) 1.00x 104m/s
D) 1.50x l04m/s
E) 2.00x 104m/s
A protonis releasedfrom restin a uniform electricfield. Theprotonaccelerates
verticallydownwardfor 5.00ps traveling5.00m. Whatis the sizeanddirectionof the
electricfield?
74.
A) 2.30N/C upward.
B) 2.30N/C downward.
-e) 4.18 x 103N/C upward
x lo3 N/c dfwnward.
6\4.18
230 x loa N/c upward.
V
75.
Let va and vs be the escapespeedsfrom Earth fortwo objectsof massesma and
rrrB: 2 mn. Determinethe ratio valvg.
A) U4
&r
E)4
A squareof side20 cm is placedon the xz planein a regionof spacewherethe electric
field is E - 300N/C (cos25" i+ sin 25" l). Whatis themagnitudeof thenet electricflux
throughthe square?
76.
/'4
A ) 3 . 1N . m 2 l c
Q)5.rN.mz/c
Cl 8.3N .mzlc
D ) 1 2N . m z / C
E ) 1 5N . m z / C
EXTRA CREDIT
Two point chargesQ and-a (a : 25.0nC) areplacedon the x-axis.The negativecharge
is at x - -2.00cm andthepositivechargeis at x : 4.00cm.Determinethe electricfield at
x : 2.00cm, on the x-axis.
77.
A) + 7.03x lOsN/C ?
( BD-7.03x ro5N/c T
,
f
t
.
t
A
)50
D) +4.22 x 105N/C ?
E) - 4.22x 105N/C ?
78.
A point chargeQ: -3.0nC is placedat distanced = 4.0 m from an infinite,insulating
sheetwith uniform chargedensityo : 40 pClmz.Find the magnitudeof the electricforce
on the point chargedueto the sheet.
A) 6.8 x 10-6N
B) 6.8 x l0-5N
-g\ 6.8 x l0-4N
a)6.8 x to'3N
N
D o.sx to-2
79.
For this question, use the samesheetand point chargeas in the previous problem. Let O
be the net electric flux through a Gaussiancube of side a : I m placed as shown in the
figure below (with two sidesparallel to the sheet),and let Ep be the magnitude of the net
electric field at point P, located on the side of the cube that is closestto the point charge.
How do these quantities changeif the point chargeis moved to the right?
@ a
A)
B)
C)
@
E)
Q increases,
Ep increases.
O remainsthe sams,Ep increases.
O decreases,
Ep decreases.
O remainsthe surme,
Ep decreases.
O remainsthe same,Ep remainsthe same.