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Physics1I
Fall 2010
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Quiz #5: Uniform Circular Motion
Problem1(2poffi)
A boy is whirling a stonearoundhis headin a horizontalcircle by meansofa shing. The string
makesone completerevolutioneverysecond,andthe tensionin the string is T. The boy then
speedsup the stone,keepingthe radiusof the circle unchanged,so tlat the stringmakestwo
completerevolutiors everysecond.What happensto the teirsionin the string?
\ pr"Ll'u '"*''" 'At4
-7-a) The tensionis unchanged.
=- rn
v,>
t')';'C
I en9toq
b) The tensionreducesto half of its original value.
c) The tensionincreasesto twice its original vslug.
d) Thetensionreducesto one-fourthofits originalvalue.
TgnS,rq = Qnlf
increases
to four timesits originalvalue.
@ Thetension
v = arle
-T
-a;
Problem 2 (3 points)
A fly landson the endof the secondhandof a clock that hasa lengthof 8.75 cm. What is the
speedandcentripetalaccelerationofthe fly?
v = aE - 2'rr(o'o??s*)
p - P.o3?5 r'r
/
-le[nd{il
Aa
tovs
Z= 6Ds
q:vz = (g,tu*lo t'/s)a
_- 4.60*16q
(4. ogns ,q)
Problem 3 (5 points)
A stuntnan is driving his motorcyclearounda vertical loop of radius
r= 15.0m at a constantspeedof 25.0mls.Thecombinedmassof the
stunfinanandmotorcycleis 185kg.
a) What is the normal force on the motorcycleatthe lantestpoinfl
^F*
Ar$,'.,-)t-P o4
it"
J
\l
+
tF
rN
r-
a Yt= mq, = n/r.
R,-*e- *u%
fn?
r
/N
m("6tv/.)
(rzsvs;
I e.ao"6"*
A=?.st*lo3N
b) What is the normalforce on the motorcycleat the ligftest point?
?l
I lN?
LJ
K
la
-lt
A"[*N
r,lb\^t\
aA
A*=. (uh-e)
+
(+# - 1-vo'/s'
tr^=tLts)s)
t
! F, =rea,= rnv/.
F^* rn?= ^u%
/
r-
N-
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