PHYSICS 1050 Mid-term Test 1 University of Wyoming 15 February 2005

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1 Name: (4 points) PHYSICS 1050 Mid-term Test 1 University of Wyoming 15 February 2005 Tis test is open-note and open-book. Tis means tat any reference material is permitted during te test. Calculators also are permitted. However, no collaboration, consultation, or communication is allowed by any means, including but not limited to verbal, written, or electronic metods. If you ave a question about te test, please raise your and. If tat does not get te administrator s attention, trow someting at im. He may try to climb across te desks to ear your question, but e will probably resort to asking you to sout across te room, since once everyone is in teir seats, it is really ard to get in or out. Please do not open tis test booklet until everyone as received a booklet and te test administrator as indicated for you to begin. Wile you are waiting, make sure tat your name is written at te top of tis page. Not only will tat get you four easy points, it will save you te trouble of trying to convince te instructor tat some ig-scoring test wit no name on it is really yours. Conversion Factors: 12 in = 1 ft 3 ft = 1 yd 5280 ft = 1 mi Pysical Constants: 2.54 in = 1 cm in = 1 m 1 lb = 4.5 N 1 day = 24 1 = 60 min 1 min = 60 s Universal gravitational constant gravitational acceleration at eart s G = Nm 2 kg 2 surface: g = 9.8 m/s 2 = 9.8 N/kg Metric Prefixes: pico: nano: 10-9 micro; 10-6 milli: 10-3 centi: 10-2 kilo: 10 3 mega: 10 6 giga: 10 9 tera: 10 12

2 Multiple coice 20 questions, 3 points eac. Please circle te most correct answer from te coices given. 1. Before te Revolution, te Frenc used a unit of lengt called te toise. Te toise was longer tan te meter. If a mountain is exactly 2000 toises ig, its eigt in meters is a. exactly 2000 meters b. less tan 2000 meters c. more tan 2000 meters 2. Te speed limit on Willett Drive by te Arena is 20 miles per our. How can tis be converted into te SI units of meters per second? 60 min 60s 5280 ft 12 in in a. 20 mi = min mi ft m mi 5280 ft 12 in in 60 min 60s b. 20 = mi ft m min mi min 5280 ft 12 in m c. 20 = 60 min 60 s mi ft in mi 5280 ft 12 in m 3600 s d. 20 = mi ft in 3. Wic of te four vectors illustrated as te largest magnitude? r r r r 4. Te proper way to add vectors A and B to obtain te vector sum A + B is sown in wic diagram below? page 2 of 12

5. Te grap to te rigt sows te progress made by a beetle moving along a straigt line. If te beetle keeps moving at te same speed, at wat time will it reac te 10-cm mark? a. 4 seconds b. 10 seconds c.

3 5. Te grap to te rigt sows te progress made by a beetle moving along a straigt line. If te beetle keeps moving at te same speed, at wat time will it reac te 10-cm mark? a. 4 seconds b. 10 seconds c. 20 seconds d. 25 seconds 6. Wen a car accelerates uniformly from rest, wic quantities increase wit time? a. acceleration and velocity b. velocity only c. acceleration and distance traveled d. velocity and distance traveled 7. A car driving in te fog rear-ends a stopped semi-trailer. Te car stops instantly, and te driver, not wearing is seat belt, impacts te steering weel. Te impact brings im to a stop in s. If te driver s air bag ad deployed, e would ave come to a stop in s. Wic of te following statements is true? a. Te driver s cange in speed is less wit te airbag tan witout. b. Te force on te driver wit te airbag is greater tan if te airbag were not tere. c. Te force on te driver wit te airbag is less tan if te airbag were not tere. d. Te air bag reduces te driver s kinetic energy more tan te steering weel alone does. page 3 of 12

8. Two balls of te same mass and moving wit te same velocity collide wit a wall. Ball A, made of soft clay, sticks to te wall. Ball B, made of rubber, bounces back from te wall.

4 8. Two balls of te same mass and moving wit te same velocity collide wit a wall. Ball A, made of soft clay, sticks to te wall. Ball B, made of rubber, bounces back from te wall. Wic ball experiences te largest cange in momentum before and after te collision? a. Ball A. b. Ball B. c. Bot ave te same cange in momentum. d. You can t tell because you don t know te time t of te collisions. 9. You are a mecanical engineer ired to design te loop-te-loop roller coaster for a new amusement park. Wat do you need to consider in your design to keep riders from falling out of te coaster at te top of te loop? a Te inward acceleration of te coaster at te top of te loop must be more tan g. b Te speed of te coaster must be greater tan terminal velocity of free fall. c Do not allow riders wo are too eavy on te coaster. d Te force olding passengers up must exceed te force pulling tem down. 10. Tere is a location between te Eart and te moon, called te Lagrange Point, were te gravitational forces from te Eart and te moon cancel. An object placed exactly at te Lagrange Point will not accelerate toward eiter te moon or te eart. Since te Eart is more massive tan te moon, te Lagrange point a. is closer to te Moon tan to te Eart. b. is exactly midway between te moon and Eart. c. is closer to te eart tan to te moon. d. is at a distance tat depends on te pase of te moon. 11. A central particle is surrounded by two circular rings of particles, as sown to te rigt. All te particles ave mass m. Wat is te direction of te net gravitational force on te central particle due to te particles in te rings? a. toward te top of te page (up) b. to te rigt c. toward te bottom of te page (down) d. to te left page 4 of 12

5 12. Te diagram to te rigt sows a person olding a ball standing at tree different places on Eart. if te person drops te ball, gravity will make it fall. Wic of te diagrams below best sows te direction te dropped ball will fall at te tree different positions? 13. My dog weigs 35 pounds. Tat means tat te Eart exerts a gravitational force of 35 pounds on my dog. Te gravitational force my dog exerts on te eart is a. 35 pounds, because of Newton s tird law. b. Less tan 35 pounds, because te dog s gravitational field is muc less tan te Eart s. c. Zero, because a dog is too small to ave gravity. d. More tan 35 pounds, but te Eart is so massive it doesn t accelerate. 14. Te mass of te planet Mars is about 1/10 te mass of Eart, and its radius is about 1/2 te radius of eart. Te weigt of te Mars probe Odyssey wen it is on te surface of Mars is a. about 1/10 its weigt on Eart. b. more tan 1/10 its weigt on Eart. c. less tan 1/10 its weigt on Eart. page 5 of 12

15. Te diagram above on te left sows a ball on te end of a string being

te diagram on te rigt sows te wirling ball as viewed from above.

Wic of tese diagrams sows te direction in wic te ball will fly, as viewed

You are riding in te rigt side of a car wen te driver makes a ard left turn.

you are accelerating outward as te car turns in a curved pat. b.

6 15. Te diagram above on te left sows a ball on te end of a string being wirled in a circle. te diagram on te rigt sows te wirling ball as viewed from above. After several wirls, te string is released wen te ball is at Q. Wic of tese diagrams sows te direction in wic te ball will fly, as viewed from above, te instant te string is released? 16. You are riding in te rigt side of a car wen te driver makes a ard left turn. You feel yourself pressing against te door because a. you are accelerating outward as te car turns in a curved pat. b. te car tilts to te rigt, so gravity puses you onto te door. c. te car is accelerating leftward as it turns, pusing into you. d. you are pusing outward on te door, so te door puses back wit an equal and opposite force. page 6 of 12

7 17. Alex is as a flat tire. Te guy at te garage, as usual, over-tigtened te nuts wen e mounted te tire, so Alex is aving trouble loosening tem. Wic direction sould Alex pus on te andle of te lug wrenc to get te maximum torque about te nut? a. straigt inward b. obliquely outward c. perpendicular to te andle d. obliquely inward 18. Te diagram below sows te positions at 1-second intervals of a ball tat is trown upward at an angle. 100 Heigt (m) Distance (m) Between te start of te ball s trajectory at (0, 0) and te end at (0, 240 m), a. te ball s kinetic energy is constant. b. te ball s kinetic energy initially decreases, ten passes troug zero and increases again. c. te ball s kinetic energy initially decreases, ten reaces a minimum value and increases again. d. te ball s kinetic energy initially increases, ten reaces a maximum value and decreases again. page 7 of 12

19. Until e was in is seventies, Henri LaMote excited circus audiences by bellyflopping from a eigt of 12 m into 30 cm of water. How can you find wat is kinetic energy KE was wen e it te water? a. Estimate is mass m, ten use KE =1 2mv 2.

8 19. Until e was in is seventies, Henri LaMote excited circus audiences by bellyflopping from a eigt of 12 m into 30 cm of water. How can you find wat is kinetic energy KE was wen e it te water? a. Estimate is mass m, ten use KE =1 2mv 2. b. Estimate is mass m, ten use KE = work = mg wit = 12 m. c. Estimate is falling power, ten use P = w t w = P t to find te work needed. d. Solve te equation = v 0 t +1 2a t ( ) 2 for v. 20. Te SI unit for energy is te joule, but power companies usually bill by te kilowatt our (kw), wic is te energy consumed by applying te power of 1000 watts for 1 our. How can you find ow many joules are equal to one kw? a W s J/s W =L b s W 1000 W J/s =L c W s J/s W =L 3600 s d W 1 W s =L J Sort answer 5 questions, 4 points eac. 21. Te diagram below sows te positions at intervals of 0.05 s of two balls moving from left to rigt. Are eiter or bot of tese balls accelerated? Explain. page 8 of 12

9 22. A skydiver jumps out of a perfectly good airplane. For a few seconds, se accelerates toward te ground, but eventually er velocity reaces a maximum value of terminal velocity, so tat er falling speed does not cange wit time. a. Identify two forces tat are acting on er body as se falls. b. In wat directions are tese two forces acting? c. Wat are te relative magnitudes of tese two forces before and after se reaces terminal velocity? 23. A feater falls more slowly tan a paperweigt. Wy? (Don t just identify te forces tat are acting on eac object; explain wy teir effects are different for te two different objects.) page 9 of 12

10 24. Te diagram sows te locations at 1-second intervals of a ball trown at 50 m/s at an angle of ~53 form orizontal. At eac location, draw a vector sowing te magnitude and direction of te ball s acceleration. (Since tere is no scale of acceleration units on te grap, you only need to make te relative magnitudes at te different locations consistent wit eac oter.) 100 Heigt (m) Distance (m) 25. Wy is it arder to open a door wen you pus near te inge tan wen you pus on te opposite side, away from te inge? page 10 of 12

11 Calculation 4 questions, 4 points eac. Te following questions require numerical answers. Sow your work, and include te units wit your answers. 26. A single force of 40 N acts upon a 5-kg block. Wat is te magnitude of te acceleration of te block? (Don t forget te units!) 27. A rifle fires a bullet wit a mass of 5.0 g (0.005 kg). Te bullet moves wit a muzzle velocity of 1000 m/s after te rifle is fired. Wat is te momentum of te bullet after te rifle is fired? (Don t forget te units!) page 11 of 12

12 28. A 100-kg mawg weigs 3000 N on te planet Druidia. Wat is te gravitational acceleration on Druidia? (Don t forget te units!) 29. A force of 50 N is applied to te end of a wrenc andle tat is 24 cm long. Te force is applied in a direction perpendicular to te andle as in te diagram. Wat is te torque (bot direction and magnitude, including units) applied to te nut by te wrenc? page 12 of 12

PHYSICS 1050 Mid-term Test 1 University of Wyoming 15 February 2005

Name: (4 points) ANSWER KEY PHYSICS 1050 Mid-term Test 1 University of Wyoming 15 February 2005 This test is open-note and open-book. This means that any reference material is permitted during the test.