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Unformatted text preview: 122. EXAM z SOLWFIous Multiple Choice. Select the best answer. No partial credit \‘J 1. What is the magnitude of the centripetal acceleration of a car in uniform circular
motion traveling at a speed of 10 m/s with a radius of 20m? 2 7— 2 2
mm? d2 , 0M5)  tow/s
SID/$2 4‘ I ’ h M
d) 3111/82 r 2.0M 20 M
e) lm/s2 f” I
7.
4 3 SMIS 2. If you see an object move in your car and you can’t identify the source of the
apparent force on the object, you are most likely in a a) noninertial reference frame
b) accelerated reference frame
c inertial reference frame Cg» both a and b
e) both b and c 3. According to Newton’s third law a) Forces act in pairs
b) For every action force there is an equal and Opposite reaction force C) F12=le
d) [Fizl = Ilel
All of the above Partial Credit Problems. Please be neat and show your work.
4. The coefficient of static friction of rubber on ice is approximately us=0.100. A
2001b woman stands on an icy sidewalk in rubber ﬂipﬂops on a cold Detroit day.
There is a horizontal force acting on the woman to the right F. a) Draw the free body diagram of the woman clearly noting the force vectors
exerted on the woman. . .1
‘4 ,1 re
+3 I F b) Apply Newton’s Second Law in both the x and y directions. 2‘11: 0 '3 F”f5 [IFZJFJl L,” \A: $5: 0 v‘ WW3 0r Wei: 1 O c) From you results in part b) calculate the magnitude of the horizontal force
F required for the woman to slip on the ice. F : (0400M2001bs) Now suppose the sidewalk is inclined as in the figure below and assume the horizontal
force F acts down the incline: 4‘"— w = 4m ——>
d) Draw the woman’s new free body diagram, clearly noting the forces
exerted on the woman. 5.
H
E
l
\
§
H
§ 6) Apply Newton’s Second Law in both the x and y directions. f) From you results in part 6) what is the new force F required for the woman
to slip in the direction down the incline? C
’2 ~14 £39: 2%] Z A?
W g) You should notice that the difference between the forces in part c) and part
13 are small (within a few pounds) even though the incline is rather steep.
Calculate the woman’s force due to gravity ALONG the incline. Is this force large enough for the woman to slip? F : Esme 3X ‘1
, k .— .914. : 1::
Stu/(E) ' T < SM 3 5. A man pulls on three blocks of mass m1, m2, and m3 connected by light strings on a
frictionless surface. The man exerts a force on the third block of magnitude F at an angle 6
with respect to the horizontal as in the image below (note: there are only two strings): a) Draw the free body diagram of each object clearly noting the force vectors
exerted on each block: ._\
V\ ___‘l b) Apply Newton’s Second Law to each block and obtain equations for the tensions
on the strings (T1 and T2), acceleration (a) and normal forces (n1, n; and n3) in both the x and y directions. c) Determine the acceleration of the system (a) in terms of m1, m2 and m3, F, and A "‘7 ~ it
Frey“: (n ’WC{ \Vl+o Z
Ffowt ‘T2 ‘2‘“ (waCt — FCOS d) What are the tensions in the strings T1 and T2 in terms of m1, m2 and m3, F, and Q , u‘bt‘VLcl CL I e) Calculate the acceleration of one block with mass m=m1+m2+m3 (the sum of the
masses of all three blocks) with the same force exerted on it. Write your answer
in terms of m1, m2 and mg, F, and 6! Compare this acceleration with your previous result (part 0). [Ma 2 (M‘+MZ&'V‘43\Q :. M
‘T\
X
\1 ...
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 Spring '08
 pope
 Force

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