KEY
PHYSICS221
EXAM 1
FALL 2OO4
QUESTIONS WORTH 2 POINTS.
Four identicalbricks of massm andlabeledA to D arearrangedas shownin the figne andmove
togetherwhenthey arepushedwith a constantforceF alonga roughsurface(with friction).
A
B
C
1.
D
Find the valueof the ratio of the net forceson blocksA andD, &gla.
F*p'
a. ll4
b. t/3
@,
d.3
e.4
2.
Block D pushesblock C with a certainforce F . The magnitudeof the force exertedby
block C on blockD is:
a.0
b.x
c.+
d.+
@f,
rnr andm2hangfrom the ceilingasshown
Two blocksof masses
in the figure.
3.
Find the tension in the string betweenthe two blocks.
a. T: mtg
fQr:-ti
\-.-/-
4.
T=(mr+mz)g
d. T: (mr - mz)g
e. T: (mz- mr)g
If the systembeginsaccelerating
upward(because
it hangsfrom the ceiling of an elevator,
for instance),the tensionin the stringbetweenthe blocks:
a. Increases
if m1 <rfi2
no matterwhat is the relationbetweenthe masses.
Gl"creases
c. Remainsthe same
d. Decreases
no matterwhat is the relationbetweenthe masses.
e. Decreases
if m1( In2
5.
The figure shows sketchesof fotr identical projectiles each launchedwith the sameinitial
speed,but with different angles. Which shell will be in the air the longest?
c)
D)
E)
A
B
C
D
All projectileswill be in the air for the sameamountof time.
6.
Which plot of a*(t) is consistentwith the v*(t) plot shownbelow?
D)
--t
€- - t-_ !o*(s)
E)
"-(t)
\o t(s)
IfA + 0thismeansthat
7.
A )e r v
B )e l vl
c )# + 0
o
a;)t*t+
-E)
trasto be changing'
lVl
A **q * : 1 kg, is tied to a roPeandis
undergoinguniform circularmotion on a
frictionteti, hotitontal table. (The figure is
view from above).Which of the following
changeswill increasethe tensionin the rope
the most?
8.
A) Doublem andhalver'
B) Doublem and doubler'
C) Doublevs anddoubler'
v6 andhalver.
@oouble
Doublevs, doublem anddoubler'
E
9.
by a
fttt ng*e showsa masssuspended
is tied
rope
The
system.
pulleyirope/chain
omut the ceiling andfloor andthe whole
systemis at rest. Which of the following is
tnre? (NOTE: T1 is the tensionin the rope
andT2 andT3 arethe tensionsin the two
chains.)
A) Tr :T2: Ta
B) Tr:T3oTr<Tz
=Tz,Tr > Tr
€.-Tt
: Ts, Tr < Tz
(- EODfz
)
T 1< T z < T s
QUESTIONSWORTH 3 POINTS.
A I .00kg stonegluedto the endof a 30.0-cmlongrod movesclockwisein a circleon a
ftictionlesshorizontaltablewith increasingspeed(fignrebelowis seenfrom above).
Directionof motion
10.
Which of the following vectorsis the bestdescriptionof the directionof the acceleration
of the stoneat the positionshownin the figrne?
A
1l.
The gluewill snapwhensubjectto a forcelargerthan50.0N. At how manyrevolutions
per minuteis the stonetravelingwhenthe gluesnaps?
a. 83.5rpm
b. I l0 rpm
@tn
rpm
d. 135rpm
e. 210rpm
Bob throws two balls A and B from the edgeof a cliffinto a plain as shown in the figure below.
Ignorepoint
Theinitialvelocitiesoftheballsdr€v6:Vli *vzj and vB:vzi,withv1,v2)Q.
P for the first two questions.
12.
Which ball will hit ttreplain first?
a.
b.
Goth
Y
e.
13
Ball A
Ball B
ballshit the groundat the sametime.
It dependson the ratio of the massesof the balls,ma/ms.
It dependson the ratio v1lv2
Find the manimumheightabovethe startingpoint that ball A will reachif
vA - (3.0i + 4.0j) n/s.
a. 0.46m
Aslm
c . 1 . 3m
d. 2.Am
e. 2.8m
14.
Point P is located7.00m awayfrom the baseof the cliff. Bob'shandis 20.0m high above
the plain. How far abovePointP doesball A pass?(Usethe sameinitial velocity asin the
previousquestion).
a.36m
b. 15m
c . 8 . 1m
.-
@2.7m
e. Ball hitsgroundbeforereaching
PointP.
I
'\
a
A smallbox of massm = 2.0 kg startsmovingup an inclineangled30" with respectto the
horizontal.The speedof the box at the bottomof the incline is 3.0 m/s, andthe magnitudeof the
box'saccelerationis 6.0 m/s2.
1 5 .Howhighverticallyabovethestartingpointdoestheboxgo?
0.20m
0.38m
0.65m
0.75m
0.87m
a.
"'J
|
d.
e.
16. Determinethe csefficient of kinetic friction betweenthe box andthe incline.
(
^
--t
b.
c.
d.
e.
,
Fk= 0.13
lrk = 0.26
Itk= 0.57
ltk = 0.93
Pt = 1.2
17.
A puck moveson a horizontal,frictionlesstablewith constantspeedv alongthe x-oris. A
constantforceF : Foj is exertedon the puck betweentr andt2. Selectthe best
descriptionof the trajectoryof the puck.
18.
it with an initial
A boatin a channelis 1000m awayfrom a wall andapproaching
of
with a marimum acceleration
velocityof 3 m/s. If the boatcanaccelerate
: I x 10-3m/s2,andthe crewtriesto preventa crash,whatwill the ship'svelocitybe
lal
when(if) it hits the wall?
,-,
S)2.6m/s
B) 2.0m/s
C) 1.5m/s
D) l.l m/s
E) Shipavoidshitting wall.
19.
A river flows southwith a speedof 20 km/hr.
If a boatcantravel at a speedof l5 km/hr
with respectto the water,at what angel,0,
will the boathaveto point so asto go straight
acrossthe river?
A) 36.9"
B) 41.4"
c) 48.6"
_4\zs.o'
C}*Oossible
for any angle.
snrT
eFrO
A ball is tossedup into the air andit comesbackto its startingpositionafter4 s. How
high abovethe startingpositiondid the ball reachat its highestpoint? Take g = l0 m/s2
and ignore air resistance.
20.
A) 100m
B) 80m
C) 50m
@3f
2t.
A 12kg block is on an inclinedplaneas.shown. Whatis the minimumvalueof static
friction, pr, neededsothat the block will not startto slide?
.--
a \ 0.42
(. B)fi.47
c) 0.s0
D) O.el
E) r.00
22. A:5?-:J+8
B:? -sj -gt
The angle betweenA and B is
A) 00
q4.
iL47'
E) 110"
23.
A particlehasa time dependent
acceleration
a(t) = (6$) t -14 S for positivet. If the
particlehasa velocityof 20 m/s at t : 0, how far will the particlemovebetweentimes
t= 0 andt: l0s?
A) 46m
B) 180m
ir3oom
( _-p / 5 0 0 m
E) 1000
m
24.
A cubicfoot of an alloyis at reston a table. Thedensityof the alloy is 7.00g/cm3
What is the size of the normal force acting on the cube?
A) 68.6N
B ) 1 . 1 8x 102N
@t.e4x
103N
D ) l . l 8 x 105N
E) 1.94x 106N
25.
A massM is attachedto a ropethat risesvertically,passesovera pulley andthenextends
horizontaltyto anothermass(or a wall). Whichropewill be underthe mosttension?
andfrictionless.
andtreatpulleyasmassless
Treatropeasmassless
B)
A)
'Crrt
)\s=/'rtn=O
FtrrcTrov)
c)
ir\s--o.l
pr.t O.ot
E) All ropeshaveequaltensions.
fs= ,}^p-a
( gr Fucrr"'o)
.l
;
EXTRA CREDIT QUESTION
26.
An objectthatmovesrapidlythroughthe air feelsa forcecalledair dragthat is similarto
friction. Air dragopposesmotionandhasa magnitud. lfo*gl : DvZ. (D is the drag
coefficient.) If we drop a ball from a very high buildingthis dragforcelimits the
maximumspeedof the falling ball. The limiting speedis calledthe terminalspeed.Use
Newton'sFirst Law, Newton'sSecondLaw and/orunit analysisto determinewhich of the
following is the correctform for terminalspeed.
B) D/IvIe
c) Ms/D
E)
1ffigo