Physics 120. Exam #1. April 15, 2011

Transcription

1 Phyc 120 Exam #1 Aprl 15, 2011 Name Multple Choce /16 Problem #1 /28 Problem #2 /28 Problem #3 /28 Total /100

2 PartI:Multple Choce:Crclethebetanwertoeachqueton.Anyothermark wllnotbegvencredt.eachmultple chocequetonworth4pontforatotalof 16pont. 1. The x-component of a partcle velocty ampled every 5 econd. The data are ft wth a traght lne a hown n the fgure to the rght. Aumng the ft a good approxmaton to the moton, whch of the followng bet repreent the x-component of the dplacement of the partcle? a. c. b. d. 2. You oberve three cart movng to the left. Cart A move wth contant peed. Cart B peedng up. Cart C lowng down. Whch cart or cart are experencng a net force to the left? a. Cart A b. Cart B c. Cart C d. Cart B and C 3. Suppoe that ntead of the Earth beng created n t preent ze and hape that t were omehow actually created twce a mave a t really wth twce the radu. The approxmate acceleraton due to gravty on th new Earth would be equal to a. g b. g 4 c. g 2 d. 4g 4. A proton accelerated from ret to a peed of 8x10 7 -m/. The momentum of the proton mot cloely 19 kgm 23 kgm 19 kgm 23 kgm a b c d

3 PartII:FreeReponeProblem:Thethreeproblembelowareworth84pont totalandeachubpartworth7ponteach.pleaehowallworknordertoreceve partalcredt.ifyourolutonarellegbleorllogcalnocredtwllbegven.a numberwthnoworkhown(evenfcorrect)wllbegvennocredt.pleaeuethe backofthepagefneceary,butnumbertheproblemyouareworkngon. 1. An object wth a ma of 2.0kg and an ntal veloctyv = 30, 42,0 m lde acro the floor (taken a the x-y coordnate ytem) pae a pont taken to be the orgn at a tme t = 0. A the object pae the orgn enter a regon of pace where t ubject to a contant frctonal force of F = 7,9.8,0 N. a. What the peed of the object and what the unt vector that pont n the drecton of the velocty? b. What the average velocty of the object between the tme t croe the pont that the orgn and the tme t come to ret? c. How long doe t take the object to come to ret? d. What the locaton of the object, wth repect to the orgn, when the object come to ret?

4 2. In a local drnkng etablhment a cutomer lde an empty mug down the counter for a refll. Momentarly dtracted, the bartender doe not ee the mug, whch lde off of the counter and trke the floor 1.4m from the bae of the counter. a. Suppoe that we take the x-drecton along the counter n the drecton the mug travelng and the y-drecton perpendcular to the counter pontng toward the celng. Startng wth the momentum prncple and ung the poton-update, wth what velocty dd the mug leave the counter f t ht the floor at a locaton r f = 1.4, 0.86,0 m from the edge of the counter? b. What the tme of flght of the projectle from the tme t leave the counter untl t reache the poton r f = 1.4, 0.86,0 m? c. Jut before the mug trke the floor, what wll be the mpact velocty? d. At what angle wth repect to the floor wth the mug trke the ground?

5 3. 65 mllon year ago a large meteorte ht the Yucatan Pennula n Mexco. The Chcxulub Impact, alo called the KT mpact, wa a 1.3x kg meteorte and beleved to be what caued the ma extncton of the dnoaur. In addton, the meteorte wa about 10,000-m n dameter and ht the Earth (ntally at ret) wth an mpact velocty of v,a = 28000,0,0 m. Studyng the mpact crater and applyng ome bac phyc allow one to deduce thee data. a. Startng from the momentum prncple, f the ma of the Earth 6x kg, what recol peed dd the Earth acqure? (Hnt: Aume that the ytem the Earth and the aterod and that after the aterod mpact the Earth, the Earth and aterod move off together at the ame fnal velocty.) b. What wa the mpule that the Earth experenced due to the mpact of the aterod? c. What wa the mpact force on the Earth due to the aterod f the aterod take 2 to collde and come to ret n the Earth crut? d. What wa the mpact force on the aterod due to the Earth f the aterod take 2 to collde and come to ret n the Earth crut?

6 Uefulformula: p = γmv 1 γ = 1 v 2 Contant g = 9.8 m 2 G = e = C 11 Nm 2 kg 2 k = 1 4πε o = Nm ε o = C 2 1eV = J µ o = 4π 10 7 Tm A c = m v v avg = + v f 2 MomentumPrncple: p f = p + F net Δt Poton update: r f = r + v avg Δt = r Vector h = J C 2 Nm 2 m e = kg = 0.511MeV m p = kg = 937.1MeV m n = kg = 948.3MeV 1amu = kg = 931.5MeV N A = Ax 2 + Bx + C = 0 x = B ± B2 4AC 2A + magntude of a vector : a = a x 2 + a y 2 + a z 2 wrtng a vector : a = a x,a y,a z p p2 m 1+ m 2 = a a ˆ = a xˆ + a ˆ y j + a ˆ z k Δt Geometry Crcle : C = 2πr = πd A = πr 2 Trangle : A = 1 2 bh Sphere : A = 4πr 2 V = 4 3 πr3