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Unformatted text preview: LPG/U 7/22»: 7‘? Sample Midterm Exam # 1
Physics 8A, Spring 2011 (Section 1) Name: Student 1]): Discussion Section: Name of Teaching Assistant: This examination has two parts. Part 1 consists of 11 multiple choice questions worth 4 points each. You need
not show your work here. No partial credit will be given for these questions.
There is no penalty for wrong answers. Part 11 consists of 3 problems. These problems each have multiple parts.
You MUST show your work for these questions. All work must be done in
this booklet. No blue books will be accepted. If you need additional paper
for working the problems on this exam, raise your hand and the proctor will
bring you paper. Make sure any additional sheets are stapled to the exam
[the proctor will have a stapler). Calculators are NOT permitted; the arithmetic is designed to be easy. You
may take ONE sheet of 8% x 11 inch paper with equations into this exam
(for the ﬁrst exam, please use only one side of the paper]. Please refer to the
fact sheet that has been distributed for information such as the sin and cos
of angles. Perfect Score Score PART 1
PART I 1 Part I: (44 points) Answer ALL the questions by Writing the letter cor
responding to the best answer next to the question. There is no penalty for
wrong answers. ' ‘ a 1. The following position vs time graph represents the motion of a toy
car. When does the car have “zero” velocity? V—‘O‘Weﬂrnf §%:a (zeros/off (a) 155 only
(b) 731
(C) '53
(d) t; and t4 only
(e) t2, t4, and t5
0‘ 2. Using the same graph as question 1, at which point does the car have
“zero” acceleration? 00/ d 3X
a = 0 mean: .: ; 0
(a) is only (and Eur/$96.: ‘ W a?“
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d e 3. Which of the following is 3 NOT a unit of acceleration?
J 4. consider the vectors A. = 3i+23dand B" : i—j‘. Which of the following best represents the vector (7 2: A — E? ‘3 ‘jk  —
‘  \Q ‘ .Ql % ~
'I
(
3 D
2 x E ‘1‘ E? y
‘5 ‘ Ut' .._\ .4, A A
A _ A A‘B *6”7)I*(2'(’U)J
Q/ : ZIP('3‘?
"2, 3 _' 
5‘ 1‘ 5. A prince is being held captive in a tower which stands 180 m above the ground. He wraps a distress message around a rock and hurls it
straight down with an initial speed of 25 m/s. After how long does the
message hit the ground? (C: :8 {NL ‘15]? fora/“Ive y d/‘rliecffan ée. a/Ownward_
s
_ 2 ' ,__ 4/ 6/47 +3!ij (a), 67/03)
(9)7.23 [‘90 :Zfd’ff'fdte [fa/am/r‘é) 3%2+fef'3v/:P' 47": “ﬂuff (s) /
(7m); fJ/IJ'I‘CHI ‘" fir} nick/d 32 52/404 7%; 7%” 5 6. A block of mass 10 kg slides down an inclined plane as shown below. if
the plane makes an angle of 37° with the horizontal and the coefﬁcient
of kinetic friction between the block and the plane is 0.1, what is the
magnitude of the frictional force? ' (a) 5.88 N 5/ d}
(b) 7.84 N \ l
(c) 9.80 N .3” ((1) zero °\
(e) 98.0 N Wm} ‘31“ a 7. A block of mass 10 kg is attached to a spring with spring constanj : 2 84¢ ) k 2 10 N/m. The spring is stretched 10 em and let go. What is th . . ?
maxnmun velomty thjljilihas. m t [0 k2 ’ d: at (I M (a .1 m/s ‘ I I E ’E . (b Jim/s n 1 A lit/4”” “(537763 .33m/s :47, => v=gd=£LEoI=alf%/ (e 10 m / s l
730 (wa’fuml /e/2 274)
e 8. A steel ball of weight W is supported b two strings as shown. Which one of the following relations must hold? )
l t
(o) 1/x/im/s lggggglﬂ' B 7 0 * 35M "jmlzwt o
l
l (a) T1—T2:2
(b)Tlsin9:W
(o) T1:Wcos9 .9“
(d)TE+T9:W 
(e) Tlsin6:T2 v,
t i: V
a 09—9.
'lw ‘t’ Tats/mo
4 ; 73th@ :72 (nape
Coffé'cf) 9. A skier of mass 60 kg goes down a slope as shown. If she starts from
rest at the top of the hill, what is her Speed at the bottom of the hill.
You may assume there is no friction 91¢
(a) 15.6 m/s K + M; : [{f 1 ’
(b) 31.3 m/s d _h l 2 500 m 3
+217 ‘ —34l'l/ + O
(c) 22 1 m/s 2 _ m/S =9 )‘c MV—"F'aPé/ffa/ryd‘ef
(e) 980 m/s : Z{30 59ft: ' $329500: 797/2 237.64%) .10. A mass is moving Clockwise at constant speed in a circle of radius 10 cm as shown. At t : 0 the velocity is 1} m/s. The acceleration at
t: 0 is: 2
l/ f
A a 0 I —,'_' : ___— :
(a) 18 m/szi A l ( ) R 0‘ 70
A W”)  . a; ,
(b) —10 Ill/522' = A W 2". J S — w A
((2)1Dm/sj 511/0 /5.2{
(d) —10 m/s?
l (e 5 III/82;: + Sm/szj 11. A mass of 5 kg feels a force F = (4 3 + 3 N. What is the magnitude
of the acceleration the mass feels? (worn/s2 J. ‘F’ , A} (bum/s2 (“Ills/"l 'Lm‘: 5 : 7 (c) 25 m/s2 (d) 5 1111/82 (e) 1/5m/s2 Part II ‘ You must show the reasoning for your aHSWers. Do this as clearly as possible
so that you may be given partial credit if your approach is correct but your
numerical answer is wrong. (Note: A neat easytoread answer is much more
likely to gain you partial credit than one we can’t decipher?) 1‘ (15 points) Note: To make the math easier, you may make the approx
 imation g m. 10 m/s. A boy throws a rock (mass : 2 kg) out a window. The Window is 20
3n above the ground and the rock has an initial Velocity: +
r7:(5§+2§)m/s' ) 7‘
i “7+ (3.) How long does it take for the rock to hit the ground? Jnu/a/nwe if Take: ‘fz‘ma affair Me rock #0 ,4/‘7‘7legroumﬂ
75M} 4/: yp/u‘ EL at;
‘20 =7 de‘j'zmdz‘a
54?)“242‘ —Zo:a 1 _ ,1 ' '
A ‘75(<jj¥4o¢)"5{7+f/o7)t5J ~3.g;(5)
(ﬂuke! fig”)! ﬂrbeJ Annyoﬂ/Jr'ca/a/pfwer) ‘ (b) HOW far does the rock travel horizontally in that time? (“r/0! )(M) ’“//+05 (2») f _
453/: Vows; _— 5.§(/+W}; 7 (Q) What is the ﬁnal Speed of the rock? n: vmr 5
V}: :4), “£4; 1' Zro§()+1/101) (d) How much work has been done by thé force of gravity during the
rock’s total ﬂight?  @raﬁvyferforw Work Mink, = ( 0) 4mg?) fax/14);)
\. ' . : —b,;4/ ‘ (we ex/ecf’ﬁﬁ 7519‘
/ orr‘fv’ve. ma #9 ably/needy”? (a! a
com/Men?‘ r9? 7%; Jung c/r‘recr’vbh 4.1 J M V}? ) L 2o :9; 2. (16 points) Masses m1 = 4 kg and m2 :ﬂkg are connected by a
massless string that passes over a frictionless pully. ml is held at rest
on the ﬂoor and m2 is held on a ﬁxed incline of 6 : 45° At time t = 0
the masses are released from rest and start to slide. Mass 7712 slides
1.00 In down the incline in 4.0 s. (a) Draw a free—body diagram for each mass (b) Determine the acceleration of each mass A72: 7.001451): 4f=¢0(s) 4 2 =W+ 5621er
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incline? ' Zf,f=7nqj/$ T,~m,j;?ﬁ,éy r——(()
Eli/:0 7‘ :9; A/: majearlﬂ' Z’iwme => We? 2;. 72 = ('2)
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é ﬂ}: = We [mpawzm‘nﬂhmdé$0,735qu) r I f [0.01/5 4/.)0/0 inlooﬁ r (d) What Is the tensmn 1n the stung? ‘ From e7». (1)) 7, = m7 +mﬂr/ = n, (g ml) 3. (15 points) A pogo stick can be thought. of as a stick with a Spring at theend. (yjeg:/0 h/rz Acre) (3) Suppose the pogo stic is standing vertically. When a boy (mass:
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the spring constant k for the pogo stick? ":lFlzzdeIoor
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, velocity when his feet hit the stick is '27 = —10j m/s. How far will
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again, pushing the boy upward. If the pogo stick transfers all Of
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