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Unformatted text preview: Name (Print) ioldns‘a la
(Last \jlgirst) ME 270  Fall 2005 Exam 2 October 27, 2005 Circle your instructor’s name/lecture time: Jones Nauman Murphy Li
MWF 9:30 MWF 11:30 TR  12:00 MWF 2:30 Please review the following statement: I certify that I have not given unauthorized aid nor have I received unauthorized aid in the
completion of this exam. Signature: INSTRUCTIONS Begin each problem in the space provided on the examination sheets. If additional space is
required, use the yellow paper provided to you. Work on one side of each sheet only, with only one problem on a sheet. Each problem is worth 20 points and may be broken into multiple parts to provide you with
ample opportunity to demonstrate your knowledge. Please remember that for you to obtain maximum credit for a problem, it must be clearly
presented. i.e. o the coordinate system must be clearly identified. 0 where appropriate, free body diagrams must be drawn. These should be drawn separately
from the given figures. 0 units must be clearly stated as part of the answer. 0 you must carefully delineate vector and scalar quantities. If the solution does not follow a logical thought process, it will be assumed in error. When handing in the test, please make sure that all sheets are in the correct sequential
order and make sure that your name is at the top of every page that you wish to have
graded. Prob. 1 Prob. 2 Prob. 3 Total Name (Print) (Last) (First) ME 270  Fall 2005
Exam 2
PROBLEM N0. 1 A massless wedge is used to move Block B (which weights 500 lb.) to the right by applying a
force, P. The coefficient of static friction between the wedge and the wall is (15: 0.20. The coefficient of static friction between the block and the floor is (15: 0.30. Frictionless rollers are
located between the wedge and Block B. a. Denote the coordinate system and draw the free—body diagrams for the wedge and the
block using the figures provided. (7 points). b. Determine the forces between Block B and the floor. Show your work. (3 points). c. Determine the force, P, that will begin to move the block to the right. Show your work. (8
points). d. If the rollers are removed (allowing friction between the wedge and the Block) what will
happen to the value for P (circle the correct answer here)? (2 points). ___.,_~ ———\< xx
/ Decrease in P No Change in P w
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Exam 2
PROBLEM NO. 2 Below is an image of a pair of ice tongs used to remove ice blocks from the ship’s hold and an
idealized pair of tongs raising a 1000 Newton ice block. Please note that the tongs have to
squeeze the ice block in order for the points to penetrate the surface of the ice, thereby enabling
the operator to pick up the block. I P
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0.20m V‘ 140 de rees \ \ I  \ g y  _ '/ (,0, “0 TN
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G) E A\Iu£‘/M.W“7 I O 55 m
" V Block of 1 F ice A I 3 j P 0 First, if the links that make up the ice tongs are assumed massless, what is the force, P.
required to maintain the system in static equilibrium. (3 points). P ; w —, logo ,4} 0 Second, draw a free body diagram of the pin at D and solve for the unknown forces. (6
points). 0 Third, draw a free body diagram of the ice block. (2 points). 0 Fourth, calculate the forces acting on link ABC. Draw all necessary free body diagrams.
(9 points). Write the force at A in vector notation. Write the force at B in vector notation. Name (Print) (Last) (First) Case :0 A
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(LaSt) (First) ME 270  Fall 2005
Exam 2
PROBLEM NO. 3 3a. A cable is wrapped around a circular tree branch. One end is attached to a load with a weight
of 237 N. It makes one complete revolution around the branch and then wraps around to the
other side where a person pulls on the cable with force, P. The coefficient of friction between the cable and the branch is 0.25. No free body diagram is necessary. (6 points total). 35 degrees Ts: "gino' + 10° +1s° : LUSS° H85“  {156° 2 SH!» “Mlrs (ozsytﬁsxc «Aims
‘72;Kz'5‘7 #3} e = l‘tcS‘N Name (Print) (Last) (First) 3b. The disk below has a triangular cut—out. Calculate the x—Component of the centroid relative to
the coordinate system given below. (8 points). L (H:n\c1’m? ._ ,. . hp 7/ ‘2"
pm  2 Thickness = U.) in. _/ 9"“
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(Last) (First) 30. A 30lb. block just begins sliding to the right when a 20lb. force is applied at the angle
shown. Determine the coefficient of friction, us, between the floor and the block. (6 points). Force 2 20 lbs. 3
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 Summer '08
 MURPHY
 Force, Friction, Jones Nauman Murphy Li

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