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WMU PHYS 1070 - Exam

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XF.0 107Physics 107 (Kaldon-23825) Name ____________________________________________________WMU - Spring 2001Exam 0F0 - 2×000,000 points Section: 10a 10b 10c 10d 10e 10fA to C D to F G to K L to N O to R S to ZRev. 4/16/99F·11/23/03SuState Any Assumptions You Need To Make -- Show All Work -- Circle Any Final AnswersUse Your Time Wisely - Work on What You Can - Be Sure to Write Down EquationsBOLDFACE Variables Are Vectors - Feel Free to Ask Any QuestionsNumbers Like 1 m/s Should NOT Be Considered 1 Significant FigureNon-Numeric Problems Should Be Short Answers!Dr. Phil's Terrible All-in-One Megadeth Roller Coaster Ride Problem (10,000 points each)1.)(a) A cable pulls the cars of a roller coaster up a 53° incline at 1.00 m/s. If the top of the first hill is 30.0 mhigh, how long does it take to reach the top? Hint: long means time here.(b) Does the cable have to support the entire weight of the cars? Draw a free body diagram first.(c) One of the roller coaster cars has a mass of 200. kg. What is the change in it’s P.E. from the bottom to thetop of the first hill? … the K.E.?(d) How much power must the motor have that pulls that cable? Hint: If you started from the top of this page,you’ve already calculated the pieces you’ll need to get an answer.(e) If the roller coaster drops all the way back to ground level at a 60° angle, can it reach a speed of 25.0 m/s atthe bottom of the hill? Assume no friction.(f) In the loop-the-loop section, the cars are going at 10.0 m/s at the top of the loop. Is a 10.0 m radius for theloop big enough so that the centripetal acceleration is greater than "g" at the top of the loop? If ac < g, then thecars aren’t going fast enough – gravity pulls the cars off of the track and they fall instead of looping the loop.(g) If a girl on the roller coaster is holding onto a hotdog with a mass of 0.0500 kg, what is the gravitationalattraction between the hotdog and the Moon a quarter of a million miles away? (mMOON = 7.36 x 1022 kg ;distance = 3.8 x 108 m)(h) A huge lighted sign advertising the roller coaster consumes 10.0 kW of 125 V electricity. Find the current,the resistance of the load, and how much energy it uses in five minutes.(i) At a height of 15.0 m and traveling horizontally at 10.0 m/s, a kid leans over the edge of the car and “loseshis lunch”. Why are you safe if you stand on the ground directly below the kid?(j) Where should you NOT stand? (Draw a sketch and calculate).(k) Looking up, a rider sees the Moon hanging up in the sky. If the roller coaster was built on the Moon, wheregravity is one-sixth that of the Earth, how much higher would that first 30.0 m hill have to be to get the samevelocity coming down? Why?(l) The engine that hauls the cars up the first hill runs at 23% efficiency, with the hot and cold reservoirs at300°C and 30°C respectively. How good of an engine is this?PHYS-107 / Final Exam (Sample) Fall 1999 Page 2(m) Lightning strikes a tree 1.00 kilometer from the roller coaster. Do you see the flash or hear the thunderfirst? Why? Approximately how many seconds will it take the sound to travel 1.00 km? Assume T = 20°C.(n) A kid 1.00 m behind you shrieks at 100 dB. At a distance of 10.0 m, the sound is 1/100th as loud. What dBis the kid’s shriek at 10.0 m?(o) Another kid on the roller coaster has a helium balloon they bought in the morning when it was 20°C. Howmuch bigger is the balloon when the temperature reaches 30°C in the afternoon?(p) At the end of the ride a friction brake is used to stop the cars, basically a piece of steel sliding on the rails.Which is important here, static or kinetic friction? Why?(q) For a 200 kg car traveling at 5.00 m/s on level track, how far will the car slide before it comes to a stop if thecoefficient of friction is 0.200? Hint: This is a nasty problem. Find the friction force first, then use Newton’s2nd law.(r) If half the car's kinetic energy goes into heating a 4.00 kg block of steel, how much will the temperature ofthe block rise?(s) At 5 m/s, what is the angular velocity of the wheels, if they are 10cm (0.1m) in radius?(t) While the car is still going 5.00 m/s to the east, a ladybug lands and starts walking south at 1.00 m/s. Findthe vector velocity rv of the ladybug, relative to the Earth. Use q = 0° for east.PHYS-107 / Final Exam (Sample) Fall 1999 Page 3Shocking (50,000 points)2.) A spark will jump a gap in air, if the electric field exceeds E = 3 × 106V/m. If lightning jumped in a straight path between the cloud and the ground,then we could figure out the potential difference between a cloud that is 1.00km (1000 m) above the ground. (a) Find V (or we could call it DV).(b) This cloud had -5.00 C of charge along its bottom, 1000 m above the ground. Suppose a charge +Q isinduced in the surface of the earth directly below the cloud, that is equal and opposite to the charge of the cloud.Find the strength of the electric force, FE, between the earth and the cloud, and explain whether the force isattractive or repulsive.(c) One of the things that we didn’t study is something called Gauss’ Law, which allows us to calculate therelationships between an Electric Field, E, and a grouping of charges in a particular shape. One of theconsequences of Gauss’ Law is that charge tends to accumulate on sharp tips, rather than on long sides ofthings. The E-field is a maximum at the tip, too. Why would this make it more likely for lightning to hit trees,church steeples, people standing out in fields, lightning rods on the roof of a barn and cows grazing on a hilltop?(d) Suppose 1.37 C of charge is moved in a lightning bolt in 0.25 seconds. What is the current, I ?(e) If the potential difference between the cloud and the ground was 100,000,000 volts, how much power wasthere in the lightning bolt in part (d)?PHYS-107 / Final Exam (Sample) Fall 1999 Page 4The Last Physics Problem for Mr. Bond (30,000 points)3.) (a) James Bond has a resistance of .007 x 108 W (that’s 7.00 x 105 W). Toescape, he hangs onto a wire carrying 1500 A of current and has a potentialdifference of 100,000 V from the ground. “You cannot escape, Mr. Bond,” saidthe evil Dr. Megaohm. “That wire you are hanging on is carrying 1500 A ofcurrent, and has a potential difference of 100,000 V with the ground.” “Ah, butI am not touching the ground,” says Mr. Bond, and he works his way along thecopper wire. “As you know, birds can walk along live


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