Unit 2 Test Review. Force, Circular Motion, and Gravity Chapters 4-5

Transcription

1 A.P. Physics B Unit Test Reiew Fce, Cicula Mtin, and Gaity Chaptes 4-5 * In studying f yu test, make sue t study this eiew sheet alng with yu quizzes and hmewk assignments. Multiple Chice Reiew: On this ptin f the test, yu will nt be allwed t use yu calculat AP fmula sheet. (Yu may, hwee, use yu AP table f infmatin.) Appximate g=0m/s f simplicity f calculatins. N patial cedit will be gien.. A pe f negligible mass suppts a blck that weighs 30N. The beaking stength f the pe is 50N. The lagest acceleatin that can be gien t the blck by pulling up n it with the pe withut beaking the pe is mst nealy... a. 6m/s b. 6.7m/s c. 0m/s d. 5m/s e. 6.7m/s. A new planet is disceed that has twice the Eath s mass and twice the Eath s adius. On the suface f this new planet, a pesn wh weighs 500N n Eath wuld expeience a gaitatinal fce f... a. 5N b. 50N c. 500N d. 000N e. 000N 3. Thee fces act n an bject. If the bject is in tanslatinal equilibium, which f the fllwing must be tue? I. The ect sum f the thee fces must equal ze. II. The magnitudes f the thee fces must all be equal. III. All thee fces must be paallel. a. I nly b. II nly c. I and III nly d. II and III nly e. I, II, and III

2 4. What is the bital speed f a satellite f mass m biting the eath at a distance fm the cente f the Eath? (Assume that G stands f the gaitatinal cnstant and M stands f the Eath s mass.) a. GM b. GM c. Gm d. Gm 5. A child has a ty tied t the end f a sting and whils the ty abe his head at a cnstant speed in a hizntal cicula path f adius R. The ty cmpletes each elutin f its mtin in a time peid T. What is the magnitude f the acceleatin f the ty? a. Ze b. 4π R T πr c. T e. GM d. g e. π g 6. Thee bjects can nly me alng a staight, leel path. The gaphs belw shw the psitin d f the bjects pltted as a functin f time t. The sum f the fces n the bject is ze in which f the cases? d d d I t t t II III a. II nly b. III nly c. I and II nly d. I and III nly e. I, II, and III 5N 7. A kg blck slides with cnstant elcity alng a hizntal tabletp. A hizntal applied fce f 0N and a dwnwad applied fce f 5N act 0N n the blck, as shwn. The cefficient f fictin between the blck and tabletp is mst nealy... a. 0.3 b. 0.4 c. 0.5 d e.

3 8. A kg bject is eleased t slide dwn a 0 incline. If the cefficient f kinetic fictin between the bject and incline is 0.4, the bject will acceleate dwn the incline at a ate f... a. (0.4)(g) b. (0.4)(g) kg (0.4)(g)(cs0 ) c. 0 (g)(sin0 ) (0.4)(g)(cs0 ) d. (0.4)(g)(cs0 ) (g)(sin0 ) e. Questins 9 and 0: A steel ball suppted by a stick is attached t a tating cylinde, and itself tates in a cicle f adius, as shwn. 9. The diectin f the net fce acting n the ball when it is in the psitin shwn is indicated by which f the fllwing? a. b. d. c. e. 0. If the ball becmes discnnected fm its suppting stick at the psitin shwn in the diagam abe, it will becme a pjectile with an initial elcity in which diectin? a. staight upwad d. t the ight b. staight dwnwad e. t the left c. ut f the plane f the page

4 Pblem Reiew: On this ptin f the test, yu may use yu calculat, AP fmula sheet, and AP table f infmatin. Patial cedit will be gien n these pblems.. The 00N light fixtue in the figue is at est. Find the tensin in the tw wies that suppt the fixtue 3 Wie 45 Wie. The cefficient f static fictin between a 3kg cate and the 35 incline it sits upn is This fictin is nt enugh t keep the bx fm sliding dwn the incline. What is the minimum squeezing fce that must be applied t the bx, pependicula t the incline, t keep the cate fm sliding? 3. An aiplane acceleates unifmly fm est. A physicist passenge hlds up a thin sting f negligible mass t which she has tied he ing and ntices that the sting makes an angle with the etical. If the plane eaches a takeff speed f 65m/s afte acceleating f a ttal f 30s, detemine the angle θ that the sting makes with the etical duing the acceleatin f the plane befe it leaes the gund.

5 4. The tw blcks in the pictue ae being held in place, and ae then eleased fm est. Use fce ideas and kinematics t find the fllwing, assuming the table and pulleys ae fictinless: the tensin in the cd cnnecting the blcks, the acceleatin f the 3kg blck as it descends, and the speed f the 3kg blck as it stikes the fl,.m belw whee it stated. 9 kg 3 kg 5. A 5cm-adius Beatles album spins at 78 e/min. What ae the magnitude and diectin f the acceleatin f a dust paticle sitting at the album s ute edge? 6. A 000kg ca unds a cicula tun f adius 30m. If the ad is flat and the cefficient f static fictin between the ties and ad is 0.67, what is the fastest elcity the ca can hae as it unds the cne withut skidding?

6 7. A lle-caste ca has a mass f 600kg when fully laded with passenges. The ehicle is appaching the tp f a hill that is shaped like pat f a cicle f adius 0m. What is the maximum speed the ca can hae when it is at the tp f the hill, in de f gaity t keep the ca n the tack? Bdy Mass (kg) Mean Radius (m) Distance fm Sun (m) Eath 5.98x0 6.37x x0 Sun 30.99x0 6.96x Mn 7.36x0 6.74x0 -- * Distance fm the Eath t the Mn = 384,000 km 8. Use the gien infmatin in the table t detemine the bital speed f the Mn aund the Eath, as well as the peid f bit f the Mn.

7 9. Actual A.P. Physics B Fee-Respnse Questin (000): m θ m M Blcks and f masses m and m, espectiely, ae cnnected by a light sting. These blcks ae futhe cnnected t a blck f mass M by anthe light sting that passes e a pulley f negligible mass and fictin. Blcks and me with a cnstant elcity dwn the inclined plane, which makes an angle θ with the hizntal. The kinetic fictinal fce n blck is f and that n blck is f. a. On the gien figue, daw and label all the fces n blck m. m θ Expess yu answes t each f the fllwing in tems f m, m, g, θ, f. b. Detemine the cefficient f kinetic fictin between the inclined plane and blck. c. Detemine the alue f the suspended mass M that allws blcks and t me with cnstant elcity dwn the plane. d. The sting between blcks and is nw cut. Detemine the acceleatin f blck while it is n the inclined plane.

8 0. Actual A.P. Physics B Fee-Respnse Questin (00): Z M R Side View: P Q A ball f mass M is attached t a sting f length R and negligible mass. The ball mes clckwise in a etical cicle, as shwn abe. When the ball is at pint P, the sting is hizntal. Pint Q is at the bttm f the cicle and pint Z is at the tp f the cicle. Ai esistance is negligible. Expess all algebaic answes in tems f the gien quantities and fundamental cnstants. a. On the figues belw, daw and label all the fces exeted n the ball when it is at pint P and Q, espectiely. P Q b. Deie an expessin f min, the minimum speed the ball can hae at pint Z withut leaing the cicula path. c. The maximum tensin the sting can hae withut beaking is T max. Deie an expessin f max, the maximum speed the ball can hae at pint Q withut beaking the sting. d. Suppse that the sting beaks at the instant the ball is at pint P. Descibe the mtin f the ball immediately afte the sting beaks.

9 Unit Test Reiew Answes:. b. b 3. a 4. e 5. b 6. c 7. b 8. d 9. e 0. c. T cs 3 = T cs 45 s T = 0.834T Als, T sin 3 + T sin 45 = 00, s substitutin gies (0.834T ) sin 3 + T sin 45 = 00 Theefe, T = 87N and T = 7.6N Fs 3(9.8) sin35. FN = = = 84.3N, s Fapp = FN Fgy = 60.N μs. 3. The acceleatin f the plane (and ing) is fund by a = 65 0 =.7m/s. 30 T calculate the angle f the sting, think abut the tw cmpnents f the tensin fce in the sting. The x-cmpnent is causing the acceleatin, T x = ma. The y-cmpnent is balancing ut the weight f the ing, s T y = mg. S θ = tan - (ma/mg) =.5 4. On the table, T=9a. F the blck hanging e the side, 9.4-T=3a. Substitutin gies a =.45m / s s T =.05N. Then the blck s final speed is fund with = + ax t be =.43m/s. 5. Fist cnet 78pm t.5m/s. Then find the centipetal acceleatin by ac = = 0.0m/s. The diectin f the acceleatin is twad the cente f the cicula path. 6. F the ca nt t skid, fictin must cause the centipetal acceleatin, s Ffic = m(ac ). Ffic =μ FN = 3,3N. S the equatin Ffic = m yields = 4.03m/s. 7. F the ca t stay n the tack, gaity must pide the fce causing the centipetal acceleatin (with F N =0 t imply that the ca is almst eady t leae the tack). S, Fg = m yields a speed f 4 m/s. 8. Gaity must be the cause f the centipetal acceleatin, F g = m, but F g is fund with Newtn s Uniesal Law f Gaitatin. This yields the expessin GmEath = which gies an bital speed f 09m/s. The peid is d π fund with the equatin = = 6 which gies T=.37 0 s, appx. t T 7.4 days. a c

10 9.a. N f m T m g F b. fic f μ= and N = F gy = mgcs θ, s μ= N mgcs θ c. Cnsideing the entie system all at nce, the fwad fces (xcmpnents f weight f blcks n the incline) ae balanced with the backwads fces (fictin and the weight f the hanging blck). mgsin θ+ mgsin θ= Mg+ f+ f 3f Sle f M = sin θ (m + m ) g d. If the sting is cut, blck will me dwn the incline unde the influence f gaity and fictin. Using Newtn s nd Law: mgsin θ f= ma mgsin θ f f and a = = gsinθ m m 0.a. P T T Q Mg b. At pint Z, using Newtn s nd law: Mg Mg + T = M R But T=0 because yu e finding the minimum speed t stay in a cicle, which wuld be the mment when the sting becmes un-tense. Sle f = gr c. At pint Q using Newtn s nd law: T M g = M R TR Sle f = gr M d. It will cntinue staight upwad, behaing as a etically-launched fee-fall bject.