Physics 2 8am solutions

Physics 2 8am solutions - L stays the same K increases<...

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Unformatted text preview: L stays the same, K increases. < Physics 2 22 April 2008 Midterm 8AM section Name. Perm #. 1. A spinning figure skater pulls his arms in as he rotates on the ice. As he pulis his arms in, what happens to his angular momentum L and kinetic energy K? C. L increases, K stays the same. D.Landeothstaythesame. ' ’* . _ 2. A deep vertical shafi penetrates to a depth that is 0.10 x the earth’s radius. That is to say, the bottom of the shaft is 0.90 x the earth’s radius from the earth’s center. The weight on the surface is wS . What is the apparent weight of an object at the bottom of the shaft compared to its weight at the surface? The mass density of the earth may be assumed to be constant. Indicate the closest answer. A. It weighs the same. 0'9' “’3 C. 0.1-wS D. 1.23-wS E 1.11-w3 3. Two bodies of equal mass, m , are rotating in outer space at a rotational velocity of (00. If the motion of the two bodies is circular, what is the separation of the two bodies? The gravitational constant isG. ’ VA 1 A. [3721]” B. There is not enough information 1 V i w U3 2 us 2 U2 W [Qty .. 6 £1 @ [22?] D [222"] E- (“:31 ‘2‘ W t :- ‘1 6 m '1... +5 wPage 1 of 8 Physics 2 22 April 2008 Midterm 8AM section Name. Perm #. 4. A small planet executes a highly elliptical orbit about a massive star. It is so massive that we ignore its motion. of the following statements are correct? M aye, "T La» flute Gk? w ’2‘: A. The angular momentum of the small planet about the star is not a constant of the motion. B. The kinetic energy of the small planet is a constant of the motion. @ The Emmy plus the potential energy of the small planet is a constant of the motion. \@ The angplar momentum of the small planet is a constant of the motion. v’ The kinetic energy of the small planet is greatest when it is closest to the massive star. _.__.__-¢ 5. Two spherical bodies have unequal mass. One is about three (3) times the mass of the other. They rotate in a circular motion — each moves in a circle bound to the other by gravity. The center of the circular motion of the light object is described by which of the following statements. A. It cannot be specified. It is at the center of mass of the heavy body. B. © It is at the center of mass of the two bodies taken together. D. It is half way between the two bodies. E. It depends on the rotational speed of the pair. 6. A steel cable is hung between two posts. It has a total mass of 50 kg. It is hung in such a way that the cable makes an angle of 45 degrees with respect to the vertical at both posts. (The cable has uniform cross section and density.) What is the tension in the cable at the either end? Choose the closest answer A. 490 N B. 683 N C. 173 N D. 347 N E. 245 N Physics 2 22 April 2008 Midterm 8AM section Name. Perm #. 7. Two steel bars, with initial equal lengths of 0.5 meter, ate jammed between two walls that we assume to be unmovable. One bar has a cross section of 1 cm2 the other has a cross section 2 cm2 The space between two walls is 0.99 meters. What is the force exerted on one wall of the walls. (An equal but opposite force will be exerted on the Opposite wall.). Assume a Young’s modulus of 20 x 101 Pascal. Find the closest answer. A. 2x105N 2.66“th é‘et c There is not enough infonnation. D. 1x105N AQZ .— _F_..__4 , 03:7. 11H!) gonna [ler +fl-Qz ' 0’0' 11' A- ALEXWSN E. 1.33 x105 N 8. A wheel and hub roll without slipping on a rail as shown. The inner hub is the part of the wheelfhub on the rail. The cable pulls with a tension T as r2 indicated on the outer part of the wheel. The radii of the wheel and hub are as shown. The moment of inertia of the wheel/hub is I and the mass is m. r; is 0., less than r;. F T Which way does the wheel/hub accelerate? A. To the Ii t. H gh ‘ T F. = w. a. To the left. d (M Q C. It can only move by slipping. V‘ D. It depends on the dimensions of the wheel and hub. ,— H .. G. I t: Y‘, "t 1 V7. " '7. i ,— it", “'1” FY) :- VI T‘(vz_—v,) —_ _.a L I/‘rI +_lM.Y,] if 5/ '4 Physics 2 22 April 2008 Midterm 8AM section Name. Penn #. 9. A right angled bracket shown to the right has equal arms 1 meter long. A force of 10 N is applied as shown. Force What is the torque applied to this object about the indicated 45° pivot point? Choose the closest answer. A. 20 N-m I pivot B. 10 N-m @ 14 N-m D. 7 N—m 499%};10. A hoop rolling along the ground behaves g3 y, like a gyroscope. Consider the action shown to the / 0‘” right. The hoop is rolling away from the viewer as shown in the “back View”. It tips slightly as shown. Which of the following statements is correct? A. The hoop continues in the same direction because the torque balances the force of gravity. \lB. A torque is applied about the point of contact with the ground in a direction into the plane of the back View figure. C. As viewed from the top the hoop rotates counterclockwise. Back View JD. As viewed from the top the hoop rotates clockwise. j E. A torque is applied about the center of mass of the hoop by the force exerted by the ground. Page 4 of 8 Physics 2 22 April 2008 Midterm 8AM section Name. Perm #. CPA/M 6014'“) M4; 11. A piece of steel cable with Young’s modulus 20 x 10‘“ Pa is 40 meters long, issuspended from one end and hangs vertically. It is 1 cm in diameter and weighs 50 kilograms. Which of the following statements is correct. A. The strain in the cable at the free end is twice the strain in the middle. is?) The strain in the attached end is twice the strain in middle. C. The strain is the same everywhere. 5?) There is no strain at the free end. B. None of the above. 12. A ladder weighing 50 lbs, unifome distributed along the length of the ladder, is jammed into the base of a wall so it can be raised by pushing upward at a point that is only Mt of the length of the ladder from the base. What is the upward force exerted to keep the ladder in the position indicated while the contractor catches her breath before pushing it all the way to the vertical. git/{LS A. Need more information. B. 50 lbs @ lQ_(Hbs F D. 200 lbs E. Olbs 45 :0 '~‘ F£W3‘503m6 Page 5 of8 Physics 2 22 April 2008 Midterm 8AM section Name. 13. and width is pulled on by a rope attached to its side as indicated. The box weighs 100 lbs. Friction keeps it fi'om sliding to the right. Which answer is closest to the tension in the rape when the box has been tipped as shown? A. Perm #. A box with equal length, height Can not find the answer without knowing the dimensions of the box and the position of the nail holding the rope end. C D. E. 14. 15. ~301bs 2: —.-. o “4M3 fifme ~601bs 2 ~ + T sue/spa ~1001bs -1“, ..L .1. ’T‘ if; ~151bs O 4 g} 2. 2' + g “T = .10 (Le a. 1 C1119: - a 31% fl’ What is the vector product of j xk ‘? E How will the weight of a body on the surface of a planet with uniform and given mass density, p , depend on the planets radius, r. A. Itwillnotdependontheradius. C. 0:1er D. ccrz E. lfr ,__——_._.___‘ («u-.- Q‘Hsfiff 04‘... Y‘ Page 6 of 8 Physics 2 22 April 2008 Midterm 8AM section Name. Perm #. ml 16. A glider of mass m1 on a frictionless horizontal __ ,' ,' " yer-J R track is connected to an object of mass 1132 by a massless ' __ K" ' string. The glider accelerates to the right, the object '5 accelerates downward, and the string rotates the pulley. - What is the relationship among T1 (the tension in the horizontal part of the string), T2 (the tension in the vertical part of the string), and the weight m2g of the object? = = _ > 3 . > . . = A. ng T2 T1 B ng T2 T19m2g>T2 Tl D D ng i"2>.'Z"l _'___._.-Q E. none of the above I 17. A disc with radius r is pinned but allowed to swing about a pivot at the disc edge. It has a mass m. The moment of inertia of the disc, about the pivot is I I = E - mr2 + mi"2 . Gravity exerts a force on the disc and it Pivot begins to rotate in a counter clockwise direction. What is the angular acceleration at this moment. a = m pa, C5 is B s C g D is Fir :- r 2 r “‘" .. a! E. None of the above. 2 ’ V‘E % Y_ a g [2' My; oz <=< "' "E 5/r 18. Two rods are made of the same kind of steel. The longer rod has a greater F length L F diameter. %> A force of magnitude F is applied to the F length 2L F end 0f each rod. Compared to the I'Od 0f E length L, the rod of length 2L has A. more stress and more strain. B. the same stress and more strain. C. the same stress and less strain. CDDess stress and less strain. .——-—-—-—-—-...-——...-——-"""" E. the same stress and the same strain. Page 7 of8 Physics 2 22 April 2008 Midterm 8AM section Name. Perm #. 19. Two bodies attracted to each other by gravity, rotate about each other with angular velocity, 0 . They have the same mass. They are separated by a constant distance d. What is the instantaneous radial acceleration of one of the bodies? A. 26:)2 id wzd / 2 C. 00' D. Need to know the mass of the bodies. E. mid. if a ,1 20. A solid cylinder rolls on the surface at constant velocity, v. It has a mass, m, and moment of inertia, I. What is the angular velocity (1) of the cylinder? 2 2 W AL 3.1, (:5 vow/z; D. Depends of the relation between the moment of inertia and the mass. E. None of the above. Page 8 of8 ...
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This note was uploaded on 05/04/2008 for the course PHYS 2 taught by Professor Freedman during the Spring '08 term at UCSB.

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Physics 2 8am solutions - L stays the same K increases<...

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