2015 Regional Physics Exam Solution Set

Transcription

1 05 Reginal hysics Exa Slutin Set. Crrect answer: D Nte: [quantity] dentes: units f quantity WYSE Acadeic Challenge 05 Reginal hysics Exa SOLUTION SET r F r a lengthass length / tie ass length / tie. Crrect answer: A Since the blck slides dwn the incline at cnstant speed, the ectr su f the Nral frce, the graitatinal frce, and the frictinal frce acting n the blck ust be zer. arallel t the incline s surface: N f g g a) f g sin 0 N g sin K erpendicular t the incline s surface: b) N g cs 0 N g cs N 90 g Diiding equatin a) by equatin b): f c) KN N K g sin g cs tan When the blck slides at cnstant elcity, the cefficient f kinetic frictin depends nly upn the angle the incline akes with the hrizntal. 3. Crrect answer: E s black bx 0.49 s s s car highway 0.00 Aerage speed accrding t the ties recrded fr the rear wheels: ae length /s tie s

2 05 Reginal hysics Exa Slutin Set 4. Crrect answer: ae(between s and s) / ae(between s and 0.49 s)? Let L represent the distance between frnt wheels and back wheels. ae fr s t s ae fr s t 0.49 s L L Crrect answer: E Using cnseratin f entu:, initial, initial, final, final Crrect answer: /s 5 t s a 9.80 /s 7. Crrect answer: A ad /s d a 9.80 /s 8. Crrect answer: A L all weight = 54.0 N Frear weight =.0 N Elbw t biceps cnnectin: x = Elbw t center f graity (c. g.) f frear: d = Elbw t ball s center f graity: L = The su f trques abut abut any pint is zer. elbw x 0.0 biceps c. g. d graity Using the elbw jint t calculate trques acting n the frear: T cs 0.0 x ccw W d cw W L cw 0 biceps frear ball

3 05 Reginal hysics Exa Slutin Set T cs 0.0 x cw W d cw W L cw 0 T biceps frear ball W freard WballL N 80N x cs cs 0.0 biceps 9. Crrect answer: F a net 369N/ x 93.7N 369N/ N 0.68kg 99 xˆ /s.0 xˆ k/s xˆ xˆ 0. Crrect answer: D The axiu speed ccurs where the acceleratin (and therefre the frce) is zer. x 369N/ 93.7N N x N/. Crrect answer: Letting dwn be the psitie directin: y y t a t y y y y /s.65 s 3.3 uzzle 30.0 Earth? after.65 s. Crrect answer: C uzzle uzzle 48 cs(30.0 ) hrizntal s s 50.3 s cs s 3. Crrect answer: A F g g a ttal F g a F g a 0.80kg /s 3.36N F 0.40 kg 0.40 kg Earth s surface

4 05 Reginal hysics Exa Slutin Set 4. Crrect answer: Since the by is ing in a circular rbit, his directin f tin is cnstantly changing. Een thugh the agnitude f his elcity (i.e., his speed) is cnstant, the by s elcity is changing because f the change in directin. The change in the elcity ectr is tward the center f the circular rbit. Therefre the by has an acceleratin tward the center f the circular rbit. Therefre, the net frce acting n the by is radially inward. 5. Crrect answer: D G F a a Earth Rrbit G R a kg Earth rbit N /s kg 6. Crrect answer: C W F d F d cs N is the angle between the frce and the displaceent. F 3.50N, east 6.00N, suth d 4.00, west kg The wrk dne by the 3.50 N cpnent is: W3.50 N, east 3.50N 4.00 cs(80 ) 4.0 J The wrk dne by the 6.00 N cpnent is: W6.00 N, suth 6.00N4.00cs(90 ) 0 The ttal wrk dne by the push is therefre 4 J. 7. Crrect answer: E The wrk dne = the change in energy f the bject. kg 5 W E Efinal Einit 0 init J s

5 05 Reginal hysics Exa Slutin Set 8. Crrect answer: E Initial V=6.00 /s kg R R A ceiling R=0.50 graity near Earth s surface spring (relaxed) Final A cpressed spring bead at rest Using cnseratin f energy: E final E kxfinal ghfinal final kxinit ghinit init kxfinal gr 0 k 0 g 0 init kxfinal gr init ( With practice, ne wuld prbably start here.) k init initial 9. Crrect answer: A gr init gr kg /s 80.7N/ xfinal R The entu f the cannn-sled-cannn ball syste is cnsered (cnstant) in the Earth frae f reference. Let: =ball, CS=cannn & sled, E=Earth, r.t.=relatie t Using the relatie elcity frula t cnert the ball s elcity t the Earth frae: r.t. E r.t. CS CS r.t. E r.t. E 63.0/s CS r.t. E Inserting this int the entu equatin: Final entu f the -CS syste = Initial entu f the -CS syste = 0 CS CS r.t. E r.t. E CS CS r.t. E 63.0/s CS r.t. E 63.0/s CS CS r.t. E CS r.t. E CS r.t. E /s 63.0/s 3.5/s CS /s

6 05 Reginal hysics Exa Slutin Set 0. Crrect answer: C y 6.00 g Find the weighted aerage f x: 60.0 (0, 0) x c Circular center bard ass = 8.00 g.00 g x x ag ag i x i ttal i.00 g5.00 c 8.00 g5.00 c 6.00 g 5.00 c+5.00 c cs g c 5.94 c 6.0g 6.0g. Crrect answer: D 8.50re 7.0 rad 0 rad re Using a frula fr rtatinal kineatics: t t rad/s t 5.0 s. Crrect answer: D The directin f the frce is in the sae directin as the acceleratin. Since the acceleratin has a negatie x-cpnent and a psitie y-cpnent, the acceleratin ectr lies in the nd quadrant. a -.0i ˆ6.0j ˆ /s tan 6.0 / angular directin = Crrect answer: E F a 4.50kg /s 90.0N 4. Crrect answer: A Trque F gr sin.45kg 9.80/s 0.80sin N leer ar R g 35.0 graity

7 05 Reginal hysics Exa Slutin Set 5. Crrect answer: The frictinal frce acts at the cntact pint between the wheel and the surface. The directin f the frictinal frce is t the left. Applying Newtn s nd Law: right F right.0n + 5.0kg 0.800/s frictin frictin frictin 5.0kg0.800/s.0N 9.00N 9.00N 9.00N frictin F right right F right left F 6. Crrect answer: A 0.800/s 3.00 s at 9.60rad/s R R 0.50 Ffrictin.0 N 7. Crrect answer: C F (N) Using: 5.0 Ipulse = change in entu and The area under a frce ersus tie graph = ipulse. area= ipulse entu 4.86/s f 3.00 s 5.0N 4.00 s5.0n 87.5Ns 8.0kg f i f t (s) 8. Crrect answer: D Gauss Law relates the net flux f an electric field thrugh a clsed surface t the net charge enclsed by that surface. 9. Crrect answer: An adiabatic prcess is a prcess in which the syste des nt exchange heat with its surrundings. 30. Crrect answer: f 365/s 89rad/s.80

8 05 Reginal hysics Exa Slutin Set 3. Crrect answer: E crawler persn crawler persn ft 4. ft 0.75ft 0.5ft 6 lb 80lb 5488lb/ft 480lb/ft 3. Crrect answer: D tp tp btt btt tp btt tp 0a tp tp btt 0a tp btt 0N/ 3 btt.8kg/ 45/s 0N/ btt 38/s 33. Crrect answer: E In the gien circuit, the 300. resistr and the 400. resistr are in parallel, and thse tw are in series with the 600. resistr. R = 400. R3 = 300. R = V R equi W 8.0 W R 77.4 equi Nte: Series resistances add, while tw parallel resistances cbine as the prduct diided by the su. (This des nt extend t three parallel resistances.) 34. Crrect answer: C The speed f a wae n a wire under tensin depends upn the tensin in the wire and the linear density f the aterial aking up the wire. T 454N 43./s 0.33kg / 5.0 t rund trip L s 43./s

9 05 Reginal hysics Exa Slutin Set 35. Crrect answer: D Cnseratin f energy: Q W QC QC TC Carnt relatinship: Q T Therefre: T Q W Q T W C Q T T C W 45 J W 6 J 47.0 C Q=45 J W=? Qc 3.0 C