Name: PHYSICS 1050 Mid-tem Test 1 Univesity of Wyoming 8 Febuay 2007 This test is open-note and open-book. This means that any efeence mateial is pemitted duing the test. Calculatos also ae pemitted. Howeve, no collaboation, consultation, o communication with othe people (othe than the administato) is allowed by any means, including but not limited to vebal, witten, o electonic methods. If you have a question about the test, please aise you hand. If that does not wok, pehaps you should just give up. Please do not open this test booklet until eveyone has eceived a booklet and the test administato has indicated fo you to begin. While you ae waiting, make sue that you name is witten at the top of this page. Convesion Factos and Constants: 100 cm = 1 m 1000 mm = 1 m 1000 m = 1 km 1000 g = 1 kg 3.2804 ft = 1 m 1 lb = 4.4482 N gavitational acceleation at eath s suface: g = 9.8 m/s 2 = 9.8 N/kg Compound Units: 1 day = 24 h 1 h = 60 min 1 min = 60 s velocity: m/s acceleation: m/s 2 foce: N = kg m/s 2 Fomulas: Aveage velocity: v = x t Instantaneous velocity: v = lim x t t 0 Aveage acceleation: a = v t Instantaneous acceleation: a = lim v t t 0 Velocity change duing constant acceleation: v = a t Distance taveled duing constant acceleation: x = v 0 t + 1 2 a ( t) 2 Acceleation fom net foce F : a = F /m momentum, impulse: kg m/s wok, enegy: J = N m = kg m 2 /s 2 powe: W = J/s = N m/s = kg m 2 /s 3 Gavitational foce on eath: F = mg Fiction: F = µn Momentum: p = mv Impulse: p = F t Wok: w = F d = E Powe: P = E t = w / t = F v Kinetic enegy: KE = 1 mv 2 2 Gavitational potential enegy: PE = mgh
Shot Multiple choice 4 questions, 4 points each. Please cicle the most coect answe fom the choices given. 1. In this class we mostly use mks units, in which compound units fo physical quantities ae expessed in tems of metes, kilogams, and seconds. Anothe popula system of units is temed cgs, in which units ae based on centimetes, gams, and seconds. The cgs unit of foce is the dyne, whee 1 dyne = 1 g cm/s 2. What is the value of 1 dyne expessed in newtons? (1000 g = 1 kg; 100 cm = 1 m.) a. 1 dyne = 1/100,000 N. b. 1 dyne = 1/1000 N. c. 1 dyne = 1/100 N. d. 1 dyne = 100 N. e. 1 dyne = 1000 N. f. 1 dyne = 100,000 N. 2. Which one of the following physical quantities is a vecto? a. Mass. b. Enegy. c. Time. d. Momentum. e. Speed. f. Distance. 3. Which one of the following statements is always tue about a scala multiple of vecto a (that is, the poduct of multiplying vecto a by a non-vecto)? a. A scala multiple of vecto a is anothe vecto eithe in the same diection as a o in the opposite diection fom a. b. A scala multiple of vecto a is anothe vecto in the same diection as vecto a. c. A scala multiple of vecto a is anothe vecto pependicula to vecto a. d. A scala multiple of vecto a is anothe vecto that can be in any diection. e. A scala multiple of vecto a is a scala. page 2 of 10
4. The foce of kinetic fiction between two sufaces sliding past each othe depends on which one facto listed? a. The coefficient of fiction µ. b. The speed at which the sufaces slide past each othe. c. The diection that the sufaces slide past each othe. d. The aea of contact between the sufaces. Matching 1 question, 4 points. 5. The diagams on the left depict the cuent velocity of an object (vecto v, line aow) and the net foce (vecto F, block aow) acting on the object. The text desciptions on the ight descibe the object's motion ove time. Match each diagam on the left with the text desciption that descibes the same pocess. F v Slowing down while changing diection. v v v F F F Slowing down without changing diection. Speeding up while changing diection. Speeding up without changing diection. page 3 of 10
Moe involved Multiple Choice 10 questions, 6 points each. Please cicle the most coect answe fom the choices given. 6. A tugboat pushes a bage along a canal at constant velocity. The only foces pushing back on the bage ae dag fom the wate and ai. How ae the foces of dag and the fowad push fom the tugboat elated to each othe? a. The (fowad) push is geate in magnitude than the (backwad) dag. b. Dag exactly equals the (fowad) push. c. Dag is exactly the opposite of the (fowad) push. d. The (backwad) dag is geate in magnitude than the (fowad) push. 7. Which one phase below coectly descibes the motion depicted in the velocity-time gaph to the ight? (Positive velocity means motion in the fowad diection.) a. Moving fowad with deceasing speed. b. Moving fowad at constant speed. c. Moving fowad with inceasing speed. d. Moving backwad deceasing speed. e. Moving backwad at constant speed. f. Moving backwad with inceasing speed. velocity 0 time 8. If the only foce acting on an object is gavity, in what diection will it acceleate? a. It will always acceleate in an upwad diection. b. It will always acceleate in a hoizontal diection. c. It will always acceleate in a downwad diection. d. It will always acceleate in the same diection as its velocity. e. It will always acceleate in the diection pependicula to its velocity. f. It will always acceleate in the diection opposite its velocity. page 4 of 10
9. When a ca tuns a cone at constant speed, so that its final diection of tavel is diffeent than its initial diection, but its speed is unchanged, how ae its momentum and kinetic enegy affected? a. Neithe its kinetic enegy no its momentum change. b. Its kinetic enegy changes, but its momentum does not. c. Its momentum changes, but its kinetic enegy does not. d. Both its momentum and its kinetic enegy change. 10. A cute fuy animal is fied fom a catapult so that flies though the ai and lands softly in a flowebed. Duing its tajectoy, the only foce acting on it is gavity. Which of the following statements coectly descibes the effect of gavity duing the animal s upwad and downwad acs? a. Gavity does positive (> 0) wok on the animal thoughout its tajectoy. b. Gavity does positive (> 0) wok on the animal duing its upwad ac, and negative (< 0) wok on the animal duing its downwad ac. c. Gavity does negative (< 0) wok on the animal duing its upwad ac, and positive (> 0) wok on the animal duing its downwad ac. d. Gavity does negative (< 0) wok on the animal thoughout its tajectoy. 11. When a commute tain moving at cuising speed applies a steady, modeate foce by its bakes, it stops in 60 s. If it bakes hade, so that its stopping foce is doubled, how long will it take to stop fom the same cuising speed? a. 240 s. b. 60 s. c. 30 s. d. 15 s. page 5 of 10
12. Fou fatenity membes each oll a keg of bee down a diffeent hill. All fou hills ae 5 m high, but they have diffeent shapes. In which case does gavity do the most wok on the keg as the keg olls downhill? a. Rolling down a steep hill. b. Rolling down a gadual hill. c. Rolling down a hill that is at fist steep, then gadual. d. Rolling down a hill that is at fist gadual, then steep. e. The wok is the same in all fou cases. 13. (We haven t talked about gavity yet, but you aleady know enough to answe this question.) The moon obits the eath instead of flying off into space at a constant velocity because the eath s gavity constantly pulls the moon towad the eath. How does the gavitational foce with which the moon pulls on the eath compae to the gavitational foce with which the eath pulls on the moon? a. The moon pulls on the eath hade than the eath pulls on the moon. b. The eath pulls on the moon hade than the moon pulls on the eath. c. The moon pulls on the eath about as had as the eath pulls on the moon. d. The moon pulls on the eath exactly as had as the eath pulls on the moon. page 6 of 10
14. A small ca (with a small mass) collides with a lage tuck (with a lage mass). The dives of the two vehicles have the same mass, and each dive stays with the vehicle thoughout the collision. How do the magnitudes of the foces expeienced by the vehicles and thei dives compae? a. The foce on the ca is geate than the foce on the tuck. The foce on the ca s dive is geate than the foce on the tuck s dive. b. The foce on the ca is geate than the foce on the tuck. The foce on the ca s dive is equal to than the foce on the tuck s dive. c. The foce on the ca is equal to the foce on the tuck. The foce on the ca s dive is geate than the foce on the tuck s dive. d. The foce on the ca is equal to the foce on the tuck. The foce on the ca s dive is equal to the foce on the tuck s dive. e. The foce on the ca is less than the foce on the tuck. The foce on the ca s dive is equal to the foce on the tuck s dive. f. The foce on the ca is less than the foce on the tuck. The foce on the ca's dive is less than the foce on the tuck's dive. 15. Which pocess equies the most powe? a. Applying a foce of 800 N at a speed of 2 m/s. b. Lifting a 500-N weight 20 m in 10 s. c. Opeating a 1000-watt hai dye. d. Acceleating a 4-kg mass fom est (0 m/s) to a speed of 50 m/s in 5 s. page 7 of 10
Shot answe and calculation 2 questions, 10 points each. Please povide complete answes to each question. Povide units with all numeical answes. Show all wok so that patial cedit can be assigned. 16. The foce diagam below depicts the foces acting on a ball on a amp. What is the diection of the amp? Daw it. Will the ball acceleate? If so, in what diection? nomal foce gavity page 8 of 10
17. A Vogon s 1 100-kg gandmothe finds heself flying though space at a speed of 20 m/s diectly towad the 300-kg Ravenous Bugblatte Beast of Taal, who is floating motionless in space. When she eaches the beast, it of couse immediately devous he. What is the Bugblatte Beasts s speed afte its dinne? 1 [Vogons] ae one of the most unpleasant aces in the Galaxy not actually evil, but bad-tempeed, bueaucatic, officious and callous. They wouldn t even lift a finge to save thei own gandmothes fom the Ravenous Bugblatte Beast of Taal without odes signed in tiplicate, sent in, sent back, queied, lost, found, subjected to public inquiy, lost again, and finally buied in soft peat fo thee months and ecycled as fielightes. The best way to get a dink out of a Vogon is to stick you finge down his thoat, and the best way to iitate him is to feed his gandmothe to the Ravenous Bugblatte Beast of Taal. Douglas Adams, The Hitchhike s Guide to the Galaxy, 1979. page 9 of 10
Exta Cedit 18. (5 points) In class, when I sang Fo acceleation, Newton s once again ou souce: It s diectly in popotion to applied net foce, But invesely to the mass of what you e pushing, of couse. what equation was I descibing? Fo full cedit, you must both name (2 pt) and wite out the equation (3 pt). page 10 of 10