Quiz2_solutions

# Quiz2_solutions - PHY 31 7K Quiz 2 1 I Some Quickies A...

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Unformatted text preview: PHY 31 7K Quiz 2 1 I) Some Quickies A hockey puck slides without friction down an icy ramp, dropping 6 meters until it slides out onto a horizontal parking lot where the coefﬁcient of friction between the puck and the ground is 0.15. 1.) How far will the puck slide before coming to rest? A.) 6 meters B.) 15 meters _ C.) 30 meters AP; GBI‘S :> T3.) 40 meters <: A carpenter’s square consists of an L—shaped piece of metal of uniform thickness where each leg is 36 inches long and 3 inches wide. 2.) Where is the center-of—mass of a carpenter’s square? lc‘ A.) At the inside corner of the L, 3 inches from the outside corner of the L as "’2 ’ ‘ _._ ( measured along each leg. :> B.) At a point between the legs of the L, 10.1 inches from the outside corner of the L as measured along each leg. 4- VP-I- ‘93 I ’ ’96}. it C.) At a point between the legs of the L, 18.0 inches from the outside corner of - 7 the L as measured along each leg. \ X C Wit“ 6 fit-53 D.) At the midpoint of one leg of the L, 16.5 inches from the inside corner of V _ the L as measured along one leg. X _ 4.” Ultra [his I“) d 1+ M E J ' - m ,r n. m "l; a \nLV In class, we had a demonstration where two students stand on separate skateboards to approximate an isolated system where there is approximately no friction between the students and the ﬂoor. The students grasp the ends of a 20 foot long rope and gently pull on it until they are next to each other. One student plus her skateboard weigh 110 pounds, while the other plus his board weigh 205 pounds. 3.) How far does the lighter student move? {7 - ~ .. . mews; A.) 7 feet [101193 >/ MS It); B.) 10 feet 1 r] .- r ' \ Sibfxﬁ _\r ‘1 :> o.) 13 feet a; Y“ “L0 6’0 W"; D.) 17 feet llf Hosf : was [Hi _. is }\/f--%- thaqnﬁy I... " '_ ~ . (Problem continues on next page.) l:— PHY 317K Quiz 2 2 {Problem continues from previous page.) A cart moving with speed 1) = 0.75 m/s on a. nearly frictionless track strikes and sticks to another cart having twice its mass that is initially at rest. 4.) How fast do the combined carts move after the collision? A.) Uni/s a» B.) 0.25 m/s <: C.) 0.5 m/s D.) 0.75 m/s m v _~, @q sewn) PHY 317K Quiz 2 3 II) A Working Elevator Consider a fast elevator carrying a load M = QOOkg up a tall building. The elevator can accelerate to its nominal operating speed ve = 4.0 m/s in onehalf the distance between ﬂoors; it decelerates to rest in the same distance. The spacing between ﬂoors is D —'—~ 3.5 m The load is placed on the elevator at the ﬁrst ﬂoor and off1 loaded on the twentieth. 5.) What is the total work W done by the elevator in lifting the load to ﬂoor 20? : : fl 11) - _ -, A.)W=0.063MJ W 3 In M“- MD“"' B.) w = 0.176 MJ :1 5*; (LU k9) . E’wygi/‘gmfg , 5a)} 7,; KO . 3’ e; o.) W = 0.587 MJ <: W : Nola l D bQCGK the, {7 5,2,1" (éjiav—E“. 5; n I,“ L l i i -. I 1 --~ ~ _ __'- : r _ x @579“ 2/ l"/N LEI? 5.5} :1 if‘frdl 1-2 gig-Baas" {Email (jiffoﬁg r f . at 5‘ {Hear 6.) How much work W; has been done on the load by thelelevator at the time is passes the second ﬂoor, now moving at full speed? , I. I. r "" _, 7‘ ‘ 2K A.) W2 : 30.9 kJ V: ME: :_ a mg L: Jr ﬁrm! 3. : 1 .1 ,ﬂ? - er _ ,._3:“; m."- ! 1| “a ELK- f t l W? 38 t 2 cm is} £3 '33:; 0 0b sift m) 0.) W2 =42.6 M f (7 I k“ D.) W2 = 69.0 1o 3; ' "x, 7.) What power P is delivered to the load by the elevator when it is moving at full speed? \' \ :;> A.) p 35.3w <: P2"; -,-;::.. n03 \[ mgng Vii B.) P : 46.8 kW " c.) P I 59.2 kW D.) P : 72.0 kW (Problem continues on next page.) PHY 317K Quiz 2 4 {Problem continues from previous page.) 8.) What is the acceleration a of the elevator when it starts out from rest? * 2 :1 t “T Q A.) Of, — IIl/S , (iii/:2 2,- d B.) 0.22.3111/52 v.6. C.) a. = 3.5 m/s2 01: ii" 31 D.) a : 4.6 111/52 <2 a :> PHY 317K Quiz 2 01 III) Grapefruit Launcher Here is an experiment you probably shouldn’t actually try: imagine an ordinary spring baiance used in a grocery store to measure the weight of produce. Assume an ideal spring, no friction, and neglect the mass of the spring and tray connected to it for holding the produce. You piece a dozen (12) grapefruit of essentially the same size and weight on the scale and notice that it deﬂects downward by 6 inches, at which point the scale measures a weight of 5 pounds. 9.) How far does the scale deﬂect with just one grapefruit on it? aria are-{1e \Lwl‘t wait-3 g W53: ‘4'; A.)Oinches . r ( fl {,7 ,. . ,l l? l W1 ft?" I a W u s. _ 5 m5 0.?) It; .3.) 0.5 inches «E: I 3 ii " I” '\ *4 “ ‘7'“ We; gmijﬁgmt . H X to l". C. 1 inch '---0 Li; , f I ) , -l--‘J“1:< 0' 9- D.) 3 inches K 0N3"; lbs-ﬂ, p5.“ Now comes the part that you shouldn’t do: with only one grapefruit on the scale, push on the scale until it indicates the same weight as all 12 grapefruit together. Then release it abruptly, causing the single grapefruit to be launched vertically. 10.) How high H will the grapefruit ﬂy? ‘1‘ 7' I1 J/ ’3 _ Ij’y‘u‘; "'7' . A.) H : 3 feet <2 if T... xx ',. r-Jf . / \x \ In (W. “I l I ‘ M x B.) H : 5feet 5 inches ﬂ— Q.f§-E§Arn)(éml_ .1 L3" 6 m C.) H = Qfeet 6inches l; gel/n3 Z). (0 HOS} D.) H = 12 feet 11.) At what reading W on the scale does the grapefruit leave the tray on its ﬂight? f, g 4‘ i-ETF‘V/Ei +149, he,” W = 0 pounds B.) W = 0.42 pounds C.) W I 5 pounds 0" lhﬂ twig GEL-<1; Inc/WE- no "ﬂea-“f. ‘1'! '. m“ "Fe-"'4 9 (“‘35-”th5 pail/ii; D.) The grapefruit never leaves the tray (Problem continues on next page.) PHY 317K Quiz 2 6 {Problem continues from previous page.) 12.) What is the spring constant k of the scale? A.) k 2 2.2 pounds/foot B.) k z 5 pounds/foot g (‘5 7 (O a (.5 {m . . \ => k : 10 pounds/foot «E: D.) k; = 12 pounds/foot PH Y 31 7K Quiz 2 IV) Cue Ball In games of pool or billiards, a one stick strikes the cue ball to set it into motion. The standard cue ball in American pool games is 2.25 inches in diameter and has a mass m = 0.170 kg. Suppose a level cue stick strikes a cue ball on a line through its exact center, imparting an impulse J = 0.24N - s to the ball, immediately after which it slides on the table Without rolling at speed vi. 13.) What is the speed iii of the cue ball immediately after being struck? Va A.) vi = 0.24 m/s 9, Em j W) (V; —‘- (5/? B.) vi = 0.85 m/s \ ' ' f1 Viztu “if: A0 ‘d\% N > _:E:_ E LIL . => Q.) vi = 1.4 III/S <: m a: k0! D.) vi : 2.0 111/5 14.) If the tip of the cue stick is in contact with the ball for At = 6 ms, what is the average force F between the tip and ball to cause the impulse J? r 7:: a 'i“ I A.)F:10N il— IL/W _ CJszN m' :WQS ‘wau :> D.) F:40N After being struck, the ball slides until friction with the pool table causes it to roll without slipping, at which point its speed is ’Ur : 1.0 m/s. Note that the moment- of-inertia about the center—of—mass of a uniform solid sphere of mass m and radius R is I = 2/5mR2. 15.) What is the total kinetic energy K of the rolling cue ball? A-) K : 0.09 J K": 1.24% ;__m\/} f Alf]: w} i B.) K : 0.12J ¢ \ N 7‘ - A, h" J‘— 3 w )‘> m\io‘ __ r1 - C.) K: 0.17} A '3 HER R} ' EX. mvo ‘l— Wit/c1 13-) K 2 0.243 mg ﬂ 7. I ":7 _ if; r: J - ﬂ 7 f \ l/ 51‘). \ " /‘ “6’? W *0 ‘7 @m/si" : K2". xiii/ {Problem continues on next page.) PHY 31 7K Quiz 2 8 (Problem continues from previous page.) 16.) Where should the cue ball be struck to cause it to start rolling immediately without sliding? :2 A.) Along a. horizontal line 0.4-5 inches above the center of the ball 4.: B.) Along a. horizontal line 0.55 inches to the right of the center of the ball C.) Along a horizontal line 1.15 inches above the center of the ball D.) There is no spot the hall where it can be hit such that it rolls without sliding New CMSeNe Mexisff-i?%U»/ﬂ (moi gﬂwgw ﬁ ’3 :- ,.. .1. g I'..‘ j m alfi'i‘v-fi‘! W?- Coglculoite angular mgmemwn “have wee may, we. I A'tfig't/ler mamemfgm z‘efii‘éyéuigeﬁ L13 l ‘ .n f ‘ Smw Miami meme J W: M'-JR+ 1w 2 MW wiw \A Unfld 31\$): TAU: ...
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## This note was uploaded on 10/14/2009 for the course PHY 317k taught by Professor Kopp during the Spring '07 term at University of Texas.

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Quiz2_solutions - PHY 31 7K Quiz 2 1 I Some Quickies A...

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