Final+2011+Solutions

Final+2011+Solutions - Final Fill in Bubble A in the Test...

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Unformatted text preview: Physics 17 2011 Final Fill in Bubble A in the Test Form box. 1. The main reason fencers stand with legs spread apart is (a) it extends their reach. ‘hey can shift their weight forward and backward without losing their balance. C 3 O WU" 5' 0‘ F F0 “f (c) that it gives them a longer lever arm for a forward thrust. (d) it raises their center of gravity (e) none of these 2. A piece of equipment discussed by Professor Ritz is . _ . 4/. @a tennis racket / (b) a surfboard (c) a snowboard (d) a ping-pong paddle (e) none of these .7 3. Hay discusses wave drag in our textbook. Which point does he not make in his discussion. (a) When a swimmer is entirely “immersed" in the air or under the water, he experiences form and surface drag of the fluid that flows by him. (b) When the swimmer comes to the surface he is no longer completely immersed in one fluid but is instead operating at the interface between two fluids. When this happens, he exerts forces that create waves. (c) The reaction to these forces, called wave drag, is a resistance force additionai to those of form and surface drag. (d) In breaststoke, even though the surface and form drag is larger, you can swim faster underwater __ because you dramatically reduce wave drag. .one of these (they are all discussed by Hay) o 9 4. Hay has a iengthy discussionfithe abiiity of a cat that is dropped upside down from rest to right itself. What point does he not make? (a) Even though the ability to do this appears to violate Newton’s laws, it should be carefully noted 1/ that throughout the whole sequence of movements the angular momentum of one body part has aiways been “matched" with an equai and opposite angular momentum of some other part. @193 falling cat is able to use torques associated with fluid drag to change its orientation. Ti}; 5 l 5 “of M a f'i‘a w‘i’ .__ (c) A blindfolded cat can not right itself as effectively as a cat that can see. I M (d) Divers and gymnasts use the same basic mechanism as the cat to alter their orientation. (6) Actually, Hay does not discuss falling cats at all. The next 3 questions concern the bounce Ufa ping-pong ball with backspin on the ping-pong table. 5. Does a ping-pong bail have a low or high coefficient of friction? 6. Is the velocity at the contact point larger or smaller than it would be if there was no spin? .ial‘ger {PM (O NV (b) smaiier (c) both the same fl ’7. Is the horizontal component of the velocity larger or smaller after the bounce than it would be without backspin? ((23 larger BackaJFo me i V \i/ ([3 smaller (c) both the same 8. Why do raceways have banked curves? (Select the best answer.) (a) The incline of the turn helps create a siingshot effect for the racecar when coming out of the turn. This helps them shoot out of the turn faster than they would coming out of an tin-banked turn. flaw We. [Ua , No aid-Sire eke—P31 +0 2? (b) Raceways have banked curbs so the car can exert centripetal and centrifugal forces to comptete I C’ V theturn. {K MIA ZR ‘5 it: i W1 G e (c) Raceways have banked curves to help counteract the force of ine a and Newton‘s First Law of$ 4“,“ 8 Motion. The banked curves lessen the force the driver must use to turn his car by making the turn a more shallow angle. N does Air. dacfaqgc 4:917:63. Raceways have banked curves because they can prevent skidding. With banked curves, the roads normal force provides a component of force directing a vehicie towards the center of the "i' PLUS curve. Banked curves reduce a vehicle’s dependence on friction to safely navigate a CUI'VE+V~ UL a (e) Raceways have banked curves in order to give the race cars more friction to stay within the line é- acifiaiij they are driving on. if it wasn’t banked, the tires would lose grip and slide out at a much lower FEAR: 5 speed compared to the banked curv The banking uses both friction and gravity to prevent the hot“! wed-a! cars from understeering out of their?i1%\ “i“? 7\ 4r t‘dq‘on :4. EL @9225 wi- +ow~n 9. The formula for rotational impulse is CA if” ‘m (b) Far (c) 'r/At (d) F/At (e) none of these ,.._'_.___,_._ FORCE a TORQUE/RADtUS woo oil VELOCIiY (Lengthwise) SPIN (Sideways) SPIN (Lengthwis VELOCITY {Sideways} _ ‘ L";A;;;seeéfifww “hiwwwmm DISTANCE {Lengthwisel The graphs in the figures describe the motion of a bowling ball down a bowling alley. The graphs show, as a function of time, (top) the force of friction and the torque associated with friction, (middle) the forward component of the translational velocity and the sideways component of the translational velocity with solid lines and the lengthwise and sideways spin with dashed line-,5 and (bottom) the lengthwise and sideways motion of the ball. (Note: the lengthwise and sideways velocities and dis- tances are not on the same scale—the sideways motion has been multiplied by a factor for clarity.) The next 3 questions concern these graphs. 10. What is the primary reason that the frictional force and torque on the ball is smaller on the part of the alley that is coated with mineral oil? (a) The normal force is reduced. (b) The coefficient of restitution is reduced. (c)“ The velocity of the ball is higher. he coefficient of friction is reduced. (e) The ball has more sideways spin. It. From the solid “VELOCITY (Lengthwise)” curve, you can tell that n33 Q‘i’i U c S [9‘9 c. '90?“ V :3) Gt 4. 0 (a) the angular acceleration is negative (in) the torque on the ball is positive (c) the component of the net force in the forward direction is positive @he component of the acceleration in the forward direction is negative (e) none of these 12. What is the sign of the torque on the ball for the lengthwise rotation? For the sideways rotation? negative Slope #0 P 5 t'aie Lewd S s pm (b) negative for both __.. < F”) ex; tale (9 ‘ 't' frlen th ' ; titef ' 'd i @031 we 0 g wrse negaa 01 st eways 32> ’t 4 O Rafi: d) negative for iengthwme; posrtrve for Sideways .‘C —-l~ slope 0“ (e) none of these 1’9“” >0 W 3*? ’b>o (a) positive for both The next four questions concern a “knock-0m ” punch in boxing. 13. A knock-out punch causes large acceleration of the head. What other quantities must be large? “(a) The force of the hand to the head F";- M 0“ W61 ‘1) W F l/éi) The change in velocity of the head Q: AV/A'f’ govt/Sgflt/ MAW ><(c) The amount oftime the fist is in contactwith the head W A'E) ism-Lt? Cl , A??? .voofthese W At M SAM/'6 (e) all of these 14. Besides accelerating the head backward, a knock-out punch jerks the head to the side. What must be true about such a punch? (a) The amount of time the fist is in contact with the head must be large. N0 @ere must be a lever arm between the axis of rotation of the head and the location where the h i' d. z; a. punc lS app 1e (ar- e, (c) The angular acceleration of the head 18 9263. M) aré (d) It must be an uppetcut. “at W MW (e) none of these T'W 0e l )e ‘ W14 W 15. (Primarily) what type of force does the punch deliver to the head? Oormal (b) Friction (e) Centrifugal (d) Fluid (e) none of these 16. One thing that must be true about the punch is 16) the force of the hand on the head must equal the force of the head on the hand Mqu‘l‘C’A/ .9 31;“ (”d (b) the impulse deliveled by the hand tow the head must equal tl e impulse delivered by the head to the hand T N Am W W 2% @0th of these keg WW 0? (d) neither of these 17. Which demonstration did Professor McWilliams include in his lecture? flbiwele wheel on a rotating spool. When the wheel is flipped over, the person holding the whee} rotates differently. (h) A bicycle connected to a motor generator and a bank of lights. A volunteer can produce about 1000 W of light. (c) An air track with two cars that collide. If one car collides with an identical stationary car and they stick together, they go about half as fast as the moving car was going. (d) A balance beam with weights. The beam wiil stay still when the torque exerted on the left side equals the torque exerted on the right side. (e) A frisbee. If a frisbee is thrown with spin it flies more stably than if it is thrown without spin. 18. Bowling balls have their mass concentrated near their center so that is . (a) the rotational inertia is large’r' Swag:- fhffi knack? c906? .Ptvkfi' .the ratio of translational kinetic energy to rotationai kinetic energy is larger :l‘V‘U—e- (c) to increase the force of friction that spins the haii ’10 erfié-d- cm. "HM g (d) to give more kinetic energy for a given transiational momentum <-—- 1&an rid; (e) none of these o R mass? U‘ at cm:- 19. A surfer wears a wetsuit to decrease n 07L f (a) radiation 'condtlction (c) evaporation 20. Two identical spherical balls collide. They exertua normal force and a frictional force on each other. Which—fereeeauses—ahorizontahimpidsel? ' - -'-"‘"‘1u‘“"‘"'-'l' (a) Normal ariction to) Both (d) Neither 21. Which is the best answer to the “Why do golf clubs have a heavy head and a light shaft?” warmup question? (a) The heavy head gives the club more centrifugal force by pulling the club outwards against the angle of acceleration. ’\ n01- deg; (~4- lpl g, (b) Golf clubs have a heavy head because a big clubhead mass decreases the impact speed. The light shaft is light so the golfer can easily swing a big are or a small arc. Q no‘f‘ 0&5.”le (c) The larger the mass that is farther away from the axis of rotation, the larger the angular acceler— ation is. No I «\l‘al‘fis I- #391; 1‘1: NoiuCQCK (d) The heavy head and light shaft allow the golfer to more effectively take advantage of the force of gravity. Furthermore, these elements decrease the club‘s rotational inertia, allowing for a faster easier stroke. £11k a. You want the rotational inertia I to be large and i is larger when there is more mass farther from 4— ‘i‘t‘u g the axis of rotation. This increases the angular momentum which enables you to give more momentum, and thus velo ity, to the golf hall. 2.3.6:; r‘r “C altefircd 'i‘i‘vxe, 22. What conditions must be satisfied for static equilibrium? (a) No net torque (b) No net force Kite—)bith of these ((1) Neither of these 23. Which statement about the “sweet spot” of a baseball bat is false? (a) The “crack” of the bat when a ball is well-hit occurs because low frequency vibrational harmon- ics are not excited when the ball is struck near the sweet spot. Tr ct g, (b) When the ball is hit near the center of percussion the handle of the bat barely moves. Trot. e, (c) When a batter is "jammed” (hits the ball near the handle), the bat stings for two reasons: 1) it vibrates strongly and 2) it jerks backward (because the bat is not struck near the center of percussion). Tr Me, (d) One reason that aluminum bats are better than wooden bats is because they have a larger coeffi- cient of restitution. Tim 6— bNone of these (they are all true). 24. In golf, there are several factors that lower the optimal launch angle relative to the 45° angle that optimizes the range for a heavy projectile. Which one does not apply? (a) Backspin gives the bail lift. 'l" l" W a“ (b) Air drag has a larger impact on the horizontal motion than on the vertical motion. 'l"? {A E— (c) The total distance of the drive includes the roll of the ball on the ground & the ball rolls farther with a low drive. +r' Ux 6.. ‘one of these (they all lower the angle). ‘glcwalgi 25. Suppose you are diving and you want to spin faster about an axis that points horizontally forward. +5“! QXt. ‘ (Assume you are presently upright & facing forward.) Which motion should you do. loatJ-‘l' k0 t‘i 7,0 V‘ A f a. (a Eomerfocuui'l' (a) Pull your legs up tight to your chest. - ‘45 ( l kt ’rW‘ (b) Pull your extended arms in tight to your chest. CL kw“) ‘5 ‘3’ . <_(c-)"Iean your head and feet to the right while shifting your hips to the left. (d) none of these 26. Suppose you are diving and you want to spin faster about an axis that points mg. (Assume you are presently upright & facing forward.) Which motion should you do? (a) Pull your legs up tight to your chest. @Pull your extended arms in tight to your chest. (c) Lean your head and feet to the right while shifting your hips to the left. (d) none of these 27. A bicycle is elevated on a stand for maintenance. After the bearings are cleaned. the wheel spins freely for a very long time. This is a consequence of which of Newton’s laws of rotation? @ewton’s lst (b) Newton’s 2nd (c) Newton’s 3rd cg F1 The running back in the figure is traveling to the right with an initial velocity ’Ufnitiat. He is about to be tackled by the crouching defensive player. The diagram to the right shows a force diagram for the running back at the time of the tackle. The next 5 questions refer to these figures. 28. Coaches advise players to tackle low because this is more effective in knocking a running back off of his feet. In physics terms, why is this good advice? low tackle has a longer lever arm relative to the center-of—gravity (cg) of the running back. 'l—l‘ Li Q... (h) A tow tackle exerts a torque on the running back that rotates his feet ch—‘clockwise. (c) both of these K (d) neither of these 29. Which way does the torque associated with F; tend to rotate the running back? (a) clockwise @ counter-ciockwise (e) neither of these 30. Which way does the torque associated with F3 tend to rotate the running back? (a) clockwise Mo [6. Va r“ a r m (b) counter-clockwise @ither of these 31. F2 is the force exerted on the running back‘s foot by the ground. The running back is wearing cleats. What type of force is this (primarily)? (a) Gravity .r wormal 4/5 W (e) Friction (d) Elastic (e) none of these 32. From the force diagram, we can conclude that, immediateiy after the tackle, the horizontal} velocity of the running back's center of gravity is h t f The he}? @0112. 44-1—6 @MW (3) tot B et M : a Wfi MW (b) to the right L @S to the right than it was before W Lérm (d) more to the right than it was before ‘A’EO'W 3 d9“) 7 L mW‘ . Mm, .. W h; A d 4 A 95$ 0; 4 (e) two of these 33. In running, it is easier to run if you pump your arms rather than keeping them by your side. Which physics concept provides the explanation for this? (a) Conservation of energy (b) Conservation of momentum (c) Air drag @ewton’s 3rd law of torques (e) None of these H003 cf / (a) (b) Vdeslred Co cred" (C) (d) thayer The figure shows a basketball player who is jumping forward with velocity replay” releasing a shot. To make the shot, the ball needs to be released with velocity 'Udesz'red- The next three questions refer to this figure. 34. To make the shot, the player needs to correct for his motion. Which dashed black arrow represents the velocity the player shouid provide when he shoots? (a) (a) ((2 [hi 3th) (C) (C) (d) (d) (e) none of these 35. What kind of spin shouid the player put on the bail to enhance his chances of making the shot, and why? ‘ @ackspin, because then a shot that hits the rim will bounce straight up. (b) Topspin, because then a shot that hits the rim will bounce straight up. (c) Backspin, because that will provide iift that increases the hang time of the shot% M (d) Topspin, because that will provide lift that increases the hang time of the shot. 36. If the player wants to hang in the air for a long time to avoid traveling, the most important quantity to increase is *— . M W wertical component of Upiayer Z (b) horizontal component of opgayer (c) magnitude of engage-r ((1) two of these (e) none of these The figure diagrams a pole vault. The height cleared is the sum of the four heights: 111, the height of the vaulter's center of gravity at the instant of takeoff; hg, the height the center of gravity is raised while he is on the pole ( the swing height); 113. the height the center ofgravity is raised once the vaulter has released the pole (the flight height); h4, the difference between the height of the crossbar and the maximum height reached by the center oi’gravity. The next 3 questions refer to this figure. 37. Just before takeoff, energy is predominately in what form? F0 in heh‘l‘ (a) elastic potential energy (b) kinetic energy P UL n m‘mj has? (0) gravitational potential energy [Up ‘wo of these (e) all of these (or none of these) 38. When the athlete’s center of gravity is at 11.4, energy is predominately in what form? (a) elastic potential energy 5 Met-i [ (b) kinetic energy P WH-‘j 5 low @ gravitational potential energy i af‘j 6"“ ((1) two of these (e) all of these (or none of these) 39. Which quantity could be negative in a world-class jump? (at) hi (1)) he @ h“! C 3 can W ((714096) :5::~ (Di—1:5 bot e (e) none of these 10 40. Knuclebails in baseball and floater serves in volleybali have unpredictable trajectories because they have large R M Z: (a) angular momentum (b) translational momentum (c) horizontal velocity (d) spin @ne of these 4 I. In a hard water polo bounce off the water, the horizontal velocity hardly changes, so we know that (a) the coefficient of restitution is large. (b) the coefficient of friction is large. (c) the coefficient of restitution is small. @he coefficient of friction is small. (e) none of these 42. Which formula is a consequence of Newton‘s 2nd law? fiAtzAp (b) 33' is constant (when no F") (0) Conservation of momentum prm; m 0 43. Two hockey players collide in midwice and stop dead. A cue ball hits the 8 ball and stops dead; the 8 ball adopts the velocity the cue ball had. These collisions are (a) both elastic (b) both inelastic (0) hockey elastic; pool inelastic @hockey inelastic; pool elastic 44. Physicists believe (a) in objective reality. (For example, natural laws like Newton’s 3rd are reproducible facts.) / (b) that successful theories are broadly applicable. (For example, the same theories apply to baseball and soccer.) . (c) in careful observation and measurement. (For example, measuring the trajectory of a tennis ball from video is used to test theoretical models.) (d) reductionist analysis yields useful insights. (For example, mentally reducing a bailerina to her \/ center of gravity helps explain her motion.) ’li of these. 11 ...
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