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Unformatted text preview: EXAM #2
PHYS 125
® 31 OCTOBER 2006 @ Name: Student ID #: $135 a} 5 t“ Part Score Short answer 2% Q 0
Problem #1 3’0 Problem #2 Honor Code Exams must be completed within the allotted time and with
no outside assistance. Instructors will periodically enter the classroom, and
you are permitted to ask questions of them. However, remember that your
instructor is limited in the amount of information he can give. There should be
no communication with any other persons (verbal, electronic, etc.) other than
the instructor. The use of calculators on the exam is permitted, but is limited
to numerical calculation. Any other uses (unit conversion, formulas, graphing,
symbolic manipulation, etc.) are not allowed. Please Sign the honor code below as conﬁrmation that you have complied
with this policy: “On my honor, I have neither given nor received any unauthorized
aid on this exam.” _ '1"! ii / "iii/f r 1 z
‘;«~"%’~7 I: / 14. Q, c." ﬂ 5' f m.“ 4.. WW7 f a, f _1, (sign%é)v" ' (date) PHYS 125
Exam #2 31 October 2006 Short Answer (40 points) Each of the ten questions below is worth 4 points. 1. A car makes a righthand turn as shown below at a constant speed. Draw
the average acceleration vector. If there is no average acceleration, indicate it with the zero vector 6. 2. A piano mover raises a IOUkg piano at a constant rate using the friction
less pulley system shown here. With how much force is he pulling on the rope? Ignore friction and assume 9 = 10 m/s2. (a) 2,000 N
(b) 1,500 N
(c) 1000 N 1‘
(d) 750 N (f) 200 N
(g) 50 N (h) impossible to determine _ PHYS 125
Exam #2 31 October 2006
——————.___._—____,__~_______ 3. In positron emission tomography, a positron and an electron annihilate at
rest producing two photons. One is emitted with the momentum vector
shown. Draw the momentum vector for the other photon. 4. A jet plane ﬂies at constant speed in a vertical circular loop. Circle the
point(s) at which the force exerted by the seat on the pilot is greatest. 5. A compact car and a large truck collide head on and stick together. Which undergoes the larger momentum change? (a) car (b) truck /
(c) The momentum c 's the same for both vehic (d) Cant tell without knowing the ﬁnal velocity of combined mass.
Which vehicle undergoes the larger acceleration during the collision?
Q (a) car /
(b truck
(c) Both experience the same acceleration. (d) Cant tell without knowing the ﬁnal velocity of combined mass. Va 1; H {g
g ..... 3;: /9‘ mm“?
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PHYS 125
Exam #2 31 October 2006
M
6. An object starts from rest, accelerating with constant tangential acceler—
ation on a Circular path. r17
Which is greater when it starts? _, 7/ Its tangential acceleration is greater;*; u xx ‘ Its radial acceleration is greater. p» i3
(c) The tangential and radial accelerations are equal. . Z)?
Which is greater after a long time? i (a) Its tangential acceleration Will be greater. / s radial acceleration will be greater
“MW—15338 radial accelerations will be equal.
7. You have a superball (a very bouncy projectile) and a spherical lump of
clay that have the exact same mass. If you can throw each at the same
speed, which would be more effective in knocking over a bottle?
"5a) The"at;tai";;""””“"' gagttggéeause it will b the bong) /
(b) The lump of clay is more effective because to the bottle.
(c) Both are equally eﬁective because they carry the same momentum
before they hit the bottle.
8. Suppose there are three astronauts outside a spaceship far away from any
planets or large masses, and they decide to play catch. All the astronauts
weigh the same on earth and are equally strong. The ﬁrst astronaut throws
the second one toward the third one and the game begins. Including the
ﬁrst, how many “throws” (not catches) will take place before the game
must end.7
(a) 1 J {w (7 IVY13) 2 a; a L‘ (C) 3 r (d) 4 (e) There is no physical reason the game should ever have to end. . / V ._ / i" f“
r  f) 6~~~ﬁ¥ ace/7 «w 7 {wiwm rrrrr ~71 " 4 ‘ tr .
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Exam #2 31 October 2006
——.~—___.__._.__—____________ Use the ﬁgure below to answer the next 2 questions. The ﬁgure shows the
potential energy function U of a particle with total mechanical energy E as a.
function of position x. 9. At what point is the magnitude of the force greatest?
At this point, does the force point in the positive or negatiyection?
(ﬂ 1:; p; it"tf‘ér’éi‘arx 10. At what point(s) is the particle moving the fastest? 5 / PHYS 125
Exam #2 31 October 2006 Problems (60 points) You must work problem #1, but you may choose to work either problem #2 or problem #3. Please circle the number of the problem you want graded on the front of the exam. If you do not, you will be penalized 2 points
__._____.___________ on the problem. 1. (30 points) The Headless Horseman is sitting atop his horse just outside
the Village of Sleepy Hollow. The Headless Horseman uses a 3.00kg jack
olantern in place of his head, and it accidently rolls off his neck from a
height of 2.50 m above the ground. The jacko—lantern strikes the ground
and bounces up to a height of 0.10 m. (a) (20 points) Find the magnitude and direction of the impulse that th round exerted on the ‘ack—o—lantern. L T _. _ < w /.
g J i 7 m. t’ 0,3? a“ tumﬂsw‘ié‘w 1; f g/ ! ' 1 ~ j L
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a it ~~”~««
or‘
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or ,,,,,,,,,,,, “A l /’ ' Li
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ngit 11%, W‘ / I _ H ’7‘ “j \/
J w A , »’ W4 ¢ “ m “‘1 Wk . c} «(we 2,»?
(b) (10 points) Below is a graph of the force delivered by the ground ‘9 m jg Ag:
the jack—o—lantern as a function of time. Note that the units on the,
horizontal axis are milliseconds. What is the value of Fmax?
Force vs. Time
Fmax
303
L2
0
0 5 10 15 20 25 30 35 40
Time (ms)
r (/1) 6
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5 Q {7/ A a. 1/ ( '
, sssss .LM/H'Mé'“ * 0*? J . v PHYS 125
Exam #2 31 October 2006
M PHYS 125 Exam #2 31 October 2006
W 2. (30 points) You are helping create a haunted house for a school carnival.
You’d like to create a spooky ghost scene in which a 2.5kg object, painted
as a ghost, is suspended from the ceiling by a 2.00—m wire and acts as a
pendulum. Initially held out horizontally from the point at which the wire
is tied, the ghost then swings freely. rm
r“‘“‘
a a 'w n4 Another volunteer tells you that they have some thin wire available that
can support tensions up to 50.0 N. However, you know from your physics
class that it if you use that wire, it will break. WW“ Find the angle 0 at which it will break. PHYS 125
Exam #2 31 October 2006
————_—__—__.________ PHYS 125
Exam #2 31 October 2006
————.—_.___~__________________ 3. (30 points) This problem extends over two pages. Two vampires,
Angelus and Spike, have a strange set of sleeping arrangements. They
sleep upside—down connected to one another by a rope attached at their
feet and slung over a pulley. Most days Angelus and Spike have the same
mass, approximately 75 kg, but today Spike has taken on an extra 10 kg
due to an all night binge on the blood of young college students. The
masses of the pulley and rope are negligible compared to our vampires’
masses, and the system is frictionless. (a) (10 points) Draw a free body diagram for each vampire, making sure
to clearly label all axes and forces. .11 , i‘ﬁihrﬂ(.yvk; N u ”) ,
'3,“
Mr 10 PHYS 125 Exam #2 31 October 2006 (b) (10 points) With what magnitude of acceleration will the system move? {w
Clay”, ff?“ : 'f/ f} {,1 :2
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g
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(c) (10 points) What is the tension of the rope on Spike’s side TS? On
Angelus’s side Ta?
f _
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9 11 Equation Sheet PHYS 125 Exam #2
M Kinematics: _, d§(t) _, t‘ _, ., A? W) = dt A305) = to) dt 71an = E _, d17(t) v, H _, a A17 W) = dt Av(t) = a(t) dt am = E 17’ = 27 V
Constant Acceleration:
As 2 vat + éasﬂkt)2 Uf’s : Um + (13131: 2a3As = via ~ v55
Circular Motion:
a ~ 0—3 a — wzr — w ~ 37:
7‘ “ r r _‘ 'Ut — w‘r — T
Forces: dg
Fnet=zZFiza§Hma .FlenB:’FBonA
.. _‘ _. _’ .1. d .. 1 _. —. _‘
lfsl S #slnl : #klnl = :u'rln' lDl '3 ZPairA’U2 lwl 2 mg FSP = —kAS
Momentum, Impulse, and Energy:
—y ti w
15': m1? J: F(t)dt J=Aﬁ
ti
1 2 1 2
K: —mv Ug=mgy USP: §k(As) Good T1319gs,tpKiqux 7 ME Mass of Earth “ “icy 1024 kg MS Mass of Sun 2 2 x 1030 kg Me Mass of electron 2 9 x 10‘31 kg Mn Mass of proton/neutron 2 (5/3) x 10“27 kg
C'e Circumference of Earth 2 4 x 107 n1 rs/e Sun—Earth separation distance 2 1.5 x 1011 In Q3 Grav. acceleration at surface of Earth 2 10 m/s2 G Gravitational constant 2 g x 10—10 N 1112/ng
yr 1 Year 2 7r x 107 3 pair Density of air at 20°C 2 1.2 kg/m3 c Speed of light in a vacuum 2 3 x 108 m/s 125 Speed of sound in 20° C air 2 340 m/s 6 Fundamental unit of charge 2 1.6 x 10—19 C
1/47T60 Electrostatic constant 2 9 x 109 N m2/C2
no Permeability constant = 47r x 10‘7 Tm/ A
BE Magnetic ﬁeld near Earth’s surface 2 5 x 10"5 T do Approximate nucleon diameter 2 2.4 fm Equation Sheet PHYS 125 Exam #2
M Binomial expansion (1 + :13)" 2 1 + 719:, for 2: << 1
l in = 2.54 cm Circumference of a circle 27r R
9 lbs 2 40 N Area of a circle 71’ R2
9 mph 2 4 m/s Volume of a sphere :1; R3
1 MeV = 1.6 x 10‘13 J Surface area of a sphere 47r R2
1 rad = 0.010 J/kg 1 Ci 5 3.7 x 1010 Bq E 3.7 x 1010 decays/s ...
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 Fall '08
 MUTCHLER

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