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Unformatted text preview: PHYS 121 (SPll) NAME (print clearly): EXAM 4 50 pts maximum Discussion Section (required): You can bring a 3x5 inch index card. Only nonprogrammable and nongraphing calculator is allowed.
Write legibly and present your solutions in an organized and coherent form. Use pencil. You must show all work, not just the answers. A correct answer alone will receive zero point. For full credit for C21, 02 and Q3, your solution must include proper diagrams, a description of your plan for solving the problem from fundamental equations, and an answer to the question posed in the
problem. Q1. Your friend is trying to raise a 7.5m—long, 50kg flagpole that has a hinge at the base by pulling on a
rope attached to the top of the pole, below is the draft his design. Since you are taking physics, he asks you to check his design. You see the rope is rated at 300 N from its package. What will you advise?
(12 pts} . trim/:1: ~"Ei‘ﬂ"Wﬁﬁlef .. A _ ——> ~_> ‘ .J .
6W Gill/Wm 5‘ $77 :7 5+9“) dim: 70) J” «in 7’“? «ﬂu Mil/a ﬁfe/N 07‘ ré’ rte/397W 02. You solved a ballistic pendulum question on Exam 3 with a light string. Now let’s modify it by replacing the light string with a thin rod with mass M/2 and length L, so here is your question. A clay ball
of mass M and speed v0 traveling in the horizontal direction strikes a block of mass 3M that’s suspended
from a thin rod with mass M/2 and length L. The moment of inertia of a thin rod of mass m and length d is md2/3 about a perpendicular axis through one of its end. 0
. . Hin e
a) Determine the speed of the clay ball just after the collusuon, g in terms of any or all of the following: up, M, L, fundamental
mathematical and physical constants. (10 pts) clung; NHFSFO’i I :56th 0 fr 144 bill/Hockm/ 1214 Hui; aid/9r Ilia/"MUM B mama? V0
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thf z) Mil/ZrT/KHWJF" :7 %:.?,Z / 63754 ‘5 09%L : : 95.“ .7715 b) Is the kinetic energy conserved during the collision? If so, why? if not, what percentage ofthe
kinetic energy is lost? (5 pts) kiwi Ills melon cvllisim, 99?;ng (Myra, Wing”? l<i = kiilﬁ : SLAM/f will“ “"B‘“ H : W} + M + km! : 3’ (Lift 1M 7‘ L4) Mix 1
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:3: {6ML){;}T_ :Sg/Viifé Z {051; 3 23k— : Fig/MU"? — ’B'j' z; Page20f4 (13. You solved an Atwood machine problem on Exam 2 by considering the
pulley is massless. The correct answer is (m2g ~ mlg)/(m1+ m). Now let’s make it more realistic by considering the pulley does have mass, so here is
your question. Atwood machine consists of two blocks of masses m1 and m2
tied together with a massless string that passes over a fixed and frictionless
pulley, the pulley has mass mp. The moment of inertia of the pulley is
mpRZ/z about a perpendicular axis through the center. A55ume m1 < m;,
find the acceleration of m1. Represent your answer in the simplest possible
form in terms of any or all of the following: m1, mg, mg, R and any universal
physical or mathematical constants. Verify that your answer agree with the
answer for the previous Atwood machine problem if you set mp=0. (15 pts) W5) mi: If W “12' “ha 1\ J] l i limp.“
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41"! _ mj TI—mrj : mm _J Page 3 of4 (14. Your little brother hands you two steel spheres. They have the same mass, the same radius and the
same exterior surface. He challenges you by claiming that one sphere is solid and the other is hollow but
there is no way you can tell. Can you determine which is which without cutting them open? If so, how? If not, why not? (2 pts) (P; , am (an, 17?” Wille MT ‘l’lfnl arm, it?” ﬁ/i’ ﬂ/atw M a” ﬂy/Mﬂ iii yet; to tie 1mm ML 75 #e 50M 72%. ﬁ/L/ s1“ A45 kg pmwf 4fmerh~a Am) 74? hollmﬂ on? I, 9; if; (Dagmar) mm /ﬁ‘%[M ﬂy/ #523 C15. A diver in the pike position (legs straight, hands on ankles) usually makes only one or oneandahalf
rotations. To make two or three rotations, the diver goes into a tuck position (knees bent, body curled
up right). Why? (2 pts) ll: NW am fr 246 M We» 3 M12; 74m
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& (myriad, (WET 7’77)” 7% W17???) a) W277 / Q6. If you are using a wrench to loosen a very stubborn nut, you can
make the job easier by using a "cheater pipe." This is a piece of pipe that
slides over the handle of the wrench, as shown, making it effectively much
longer. Explain why this would help you loosen the nut. (2 pts) Ag torrid/c7 m M {[5 g fng
éjlﬁtﬂW 79ml ([2 PM: f?ch Fri/[mes r/g {075,5 #6 we" law/cw. an away we 1;.) a7.» Q7. A uniform rod pivots about a frictionless, horizontal axle through
its center. It is places on a stand, held motionless in the position shown. What’s going to happen if it is gently re ' oing to
rotate clockwise, rotate counterclockwise or, o rotation at all. (2 pts) Page 4 of 4 ...
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 Fall '07
 Angerson
 Physics

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