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Unformatted text preview: EXAM #1
PHYS 125
20 SEPTEMBER 2005 Jbvom \_ Wm, H,~..cxw.§ Name: F
(please print legiblﬁ) Sow“: 2.0523 Student ID #: Part Score Tl
’(T Short answer 1 Problem #1 H 0
Problem #2 Problem #3 D )7
Total Q P 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 calculation. Any other uses (unit conversion, formulas, graphing, 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.” .
5% {/2535}? (date) (signature) ‘i/vx PHYS 125 Exam #1 20 September 2005 Short Answer (40 points) Each of the ten questions below is worth 4 points. x {We’ll learn in Chapter 12 that the period of a planet around the sun could (“k/conceivably depend on three things: the the sun M, the planet is fromgthgewsun R, and a universal constant called Newton’s
gravitational constant 777G , The gravitational constant has dimension of Use dimensional analysis to ﬁnd a relationship for the time of orbit using
some combination of M, R7 and G. i/gﬁﬂp_ﬂ,w,_w. K‘H‘A“ ‘ M t ‘ MN“ _ 4
T 2 is ‘ . ,5.  i \ . a .t. v. r i
ii wit A y Mg K a TM. a b 23
W l, 5 A? r V"  t ‘
\.  . : 2. To avoid falling too fast during a landing, an airplane mus
minimum airspeed (the speed of the plane relative to the air). However,
the slower the ground speed (speed relative to the ground) during a land
ing, the safer the landing. Is it safer for an airplane to land with the wind
or into the wind? 3. Your physics instructor stands in class and throws a ball in the air such
that it undergoes freefall motion as in the ﬁgure below. What is the
acceleration at point 4? oar, Rapier»: ‘3 Wfi { $7 4. Can velocity be changing While speed is constant? {gs’EO/rg/ Can speed be changing while velocity is constant? yes or r r x PHYS 125
Exam #1 20 September 2005 5. A wooden block of some length is twice as wide as it is thick. Which ori— entation of the block once laid upon a wooden inclined plane has a bigger
coefﬁcient of static friction? (a) 1
(b) 2
1 p
K: ey’re the same.
(d) There is not enough
information
2 6) Below is a depiction of the earth as it orbits the sun in a full year. Please
draw the average velocity vector between Aggggpéand 20 Sep 2005 and label it 17%. Pleas draw the instantaneous velocity vector at 20 Sep 2005
and labelgit 17. 20 Dec 2004 3 2] Jun 2005 % 04 Feb 2005 06 May 2005 ® ® 2! Mar 2005 3 7. An object goes from one point in space to another. After it arrives at its
destination, its displacement is: (a) either greater han or equal to (b) always gr ter than ' her smaller than or equal to
(e) always smaller than (f) either smaller or larger than the distance it traveled. PHYS 125
Exam #1 20 September 2005 8 ‘ Below is a depiction of the moon as it orbits the earth in a 28—day cycle.
Please draw the average acceleration vector between 13 Sep and 20 Sep
and label it ﬂavg. Please draw the instantaneous acceleration vector at 20 Sep and label it (1'. 0486p, @ 9. A car is traveling forward around a banked curve at a constant speed so
fast that it is about to slip. Please use the ﬁgure at right to draw all the
forces acting on the car, You may neglect air drag. to answer the following questions: In which region(s) is e s p i cart’s acceleration negative? Circle all
that apply. 1 2 ;_ 4 6 7 none In which region(s) is the shopping cart’s di 3 nt negative? Circle all
that apply. 1 PHYS 125
Exam #1 20 September 2005 Problems 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. 1. (40 points) You are asked to consult for Houston’s M. D. Anderson hospi
tal, where a group of doctors is investigating the bombardment of cancer
tumors with high—energy ions. The ions are ﬁred directly toward the cen
ter of the tumor at speeds of 5.0 x 106 m/s. To cover the entire tumor
area, the ions are deﬂected sideways by passing them between two charged
metalplatesthataceelerate thelionspewrpendicular totheﬂdirgction of their 10,1? nay/32., The acceleration region is 5.0 cm long,
and the ends of the acceleration plates are 1.5 m from the patient. How far
will the ion deﬂect across the tumor d? You may neglect any accelerations . §»
, ( (o ‘ 5(tf, \ 1,
due to gravrty. { >3 4 : Sf m ‘4: wk , ,‘V‘lﬁ V i f
acceleration
, plates ,1,» r 
x/ ‘21; J {V V J
, 'o
W k...) , 1x)
\A :9 “K n Iii}: ' by 2.? ‘0 K
‘.n z
, n», 53 v ' ~ » ‘ A!“ ” i
[\
JR 3 "j\ /
t J,» 1’
:0 fr _ *1“, ‘ A
irka \32 \Alx ‘1'») “ ‘
i)
W V t m r' sxvu‘oi‘wff o’K "i ‘5‘ Jv ‘32., 1 O. or: raw +r
u — > '“ L
J2, ﬂ h
\.,MN__M._~z—~ F Y» I R CV,"
(«1,
{a 4 +1,  \ \_ l X\»KQ L \Juc V C'Aw ‘” v S“ CM PHYS 125
Exam #1 20 September 2005 2. (40 points) One of Napoleon’s skills is playing “tetherball.” Tetherball is
very simple. It consists of hitting a ball that is attached to the top of a pole by a string. See re psi/(Dylkmw
Napoleon hits a 0. k 1th‘av force of 10 Wef time
such that after leaving his hand it‘m yergoes Circular motion round t e pole. If the lm lon string makes an angle of 30a WILETEEBEIe, for what
amoun 0 time did Napoleonndweliver the force? “n.7,... r (3.) Begin by drawing a free—body diagram for the ball some time after it
leaves Napoleon’s hand and is undergoing circular motion. (b) Solve for the tension in the string. ((3) Solve for the speed of rotation. (d) Assume that the ball has held at rest and then accelerated up to
its speed of rotation to ﬁnd the amount of time for which Napoleon
applied his force. 3 2
"I
Y N
(313; M ‘2; F; v.55) 0” ?s°
. w J? ~
,1,
\(J‘ \\9 3 t /) (b) Use Newton’s Second Law to ﬁnd the coefﬁcient of static friction ,us
( gawk ﬂ . M" G between the hand and gurney.
, S: 4 l I
F: WAC“ ‘> A} 3
Ft} W‘d Fig, 1 vex, :0
‘Ns‘z ‘5 Ni! u; ?‘ D7 ‘4 Li » Uni ?/ {is t 0 (2 it?) . if"; 7 8w“ 5, 5»! E», A"? ‘4 N~ (mi/y “3:3: '3 PHYS 125 Exam #1 20 September 2005 ? 3. (40 points r. Quincy sits in the coroner’s ofﬁce thinking of how much
‘ e would have been had his Ina” sics, So he decides
to do an experiment to ﬁnd the coefﬁcients of frictio between a severed hand and a stainless steel gurneyf ‘M’ MM,_ .......... ~.M‘M.~,,_._..n .4...“ . Dr. Quincy ﬁnds that he mustﬁraise one end of the 2—rn long gurney 1 111
before the severed hand begins to slide. And it takes 15 s for the hand to reach the bottom. (a) Begin by drawing a free body diagram representing all the forces
acting on .,_ (r M: ' “1 » . / .\'!'\)(?u§ WWW“
N“‘°'7/§(°‘U ) l6.‘l£:ﬁ’~=
t; [\j i: {irve—l‘Lw N l‘: i ii «A
(c) What acceleration does the hand experience on its way down the
gurney?
F: W R Z! :;M : (0.31“) a, J" (W A ‘4‘: .M @se Newton’s Second Law to ﬁnd the coefﬁcient of kinetic friction ,uk
».// etween the hand and gurney. Pk, "Mb N N PHYS 125
Exam #1 20 September 2005 Name: E lg KM“: )KQE l ID: 3(b l S 7’ S Q
Exercise Step Max Score 1 Solving for T o< 1/R3/(GM) 4
T o< G‘l/2 1 T o< M“1/2 1 e
T OC R3/2 1 7/
T oc nothing else 1 l
2 Into the Wind \ 4 lg Ll
3 Acceleration at 4 4
g or 2 9.8 m/s2 2 I
no units on 2 9.8 —1 O
direction, either “down” or a minus sign 2
4 Velocity vs. Speed 4 I
v constant, “yes” 2 27 constan , “no” 2 ‘
5 us is the same (c) 4 6 17an vs. 17 4
17an points from 05 Aug to 20 Sep 2 CD 17 points horizontally to the left 2 7/
7 Displacement S distance, (d) 4 L! L\
8 6m”; vs. 53 4
5an points down and to the right at N 45° 2 (L L‘
(1’ points vertically down 2 9 Banked curve FBD 4
Weight (W, 135,, m 57) points straight down 1 L/
Normal , 151V) points J. out of incline 1
Friction (Ff, Ff“ points down incline 1
N 0 other forces 1
10 Shopping graph 4
part 1 3 and 5 2 ’
Include a 5’ or 5 I l [/
part 2 none 2
if (5, 6, and 7) 1
Total 40 Exam #1 Problem Steps 1 Solving for Atl Apply A$1 Z 1102: A151 + $01 Ail?
Mathematics/Substitution Atl = Ala/110 210‘8 3 Solving for my Apply vly = 00;, + my Ah
Mathematics/ Substitution
'Uly = (11!, Atl : 5 X104 III/S Solving for Ayl, but not my
Apply Ayl : pay Atl + éaly A1512
Mathematics/Substitution A341: éaly Atlz = 2.5 X 104 m Method #1 Solving for At; Apply Ax; = v1z Atz + éal At22
Mathematics/Substitution Atz = Ala/110 = 3 X 10—7 S Solving for (1 Apply Ayz = Uly Atz + éazy N22
Mathematics/Substitution d = my Atz +[Ay1] = 1.5 ><10‘2 m Correct units Method #2
Solving for tan 0 Apply tang 2 3”
Mathematics/ Substitution tanH 2 v7? :10“2 PHYS 125
20 September 2005 Max Score 140 E/lp 20 S no 4: NutAb HNMC.“ 1H Solving for d 10 Apply tanQ = gig—ill 4 _ Mathematics/Substitution 4 __ d 2 tanBAl‘z + [Ag/1] = 1.5 ><10“2 m 1 __ Correct units 1 ___
Total 40 PHYS 125 Exam #1 20 September 2005
Problem Steps Max Score
2a Free Body Diagram 11 Tension drawn correctly 3 Weight drawn correctly 3 No other forces drawn 3 Axes labelled 2 2b Solve for T \ 7
Apply Fj’et = may to ﬁnd T 2
Mathematics / Substitution 3 T 2 £55 2 5.7 N 1 Correct units 1 2c Solve for v 12
Apply F3; 2 mar to ﬁnd ac 2 Apply ac = 11—77372? to find 1) 2
Mathematics / Substitution 6
v=sin6‘/E%S—L—21.7m/s 1 Correct units 1
2d Solve for At 10
Applszmatoﬁnda 2 Apply 1) = 110 + a At to ﬁnd At 2
Mathematics / Substitution 4
At="}—::8,5x10‘25 1 Correct units 1
Total 40 Problem Steps 3a 3b 3c 3d Free Body Diagram
Normal force drawn correctly
Weight drawn correctly
Friction drawn correctly No other forces drawn Axes labelled Solve for p, Apply Fj’et 2 may to ﬁnd N
Apply Ffe‘ = max to ﬁnd F;
Apply F5 S #5 N to ﬁnd #5
Mathematics/Substitution _ __ 1m __
#5 — tanH _ (huhum)? —_ 0.58 Correct units Solve for 0 Apply As = 1103 At + %a5 At2 to ﬁnd a
Mathematics/Substitution a. = 2fef 2 1.8 m/s2 Correct units Solve for pk
Apply 1‘7""at : maI to ﬁnd FR 1’]
Apply Fk = pk N to ﬁnd pk
Mathematics/Substitution lukzpk/N: W 20.37 m 9 cos 0
Correct units Total Max Score 10 NMMMN r— HODNNM'; l—‘HMMUJ HHuhMNS 4O PHYS 125 Exam #1 20 September 2005
W ...
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 Fall '08
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