Physics 107 / Exam 2 [Form-A] Summer I 2007 Page 2“First Problem” (30,000 points) Multiple-Guess-Pick-The-Best-Answer-Fill-In-The-Bubbles1.) (a) If you want the fastest acceleration in a car, you must use _______ friction.A = Static B = Kinetic C = Potential D = Radial InwardE =Tangent F = Radial Outward(b) For an object undergoing Uniform Circular Motion, the velocity vector is _______ to the circular path.A = Static B = Kinetic C = Potential D = Radial InwardE =Tangent F = Radial Outward(c) A rock dropped from the top of a building will gain in _______ and … A = Static B = Kinetic C = Potential D = Radial InwardE =Tangent F = Radial Outward(d) … lose in _________ Energy.A = Static B = Kinetic C = Potential D = Radial InwardE =Tangent F = Radial Outward(e) _________ Energy must change if a net force does work on a body.A = Static B = Kinetic C = Potential D = Radial InwardE =Tangent F = Radial Outward(f) The old trick of starting a fire by rubbing two sticks together uses ___________ friction to generate heat.A = Static B = Kinetic C = Potential D = Radial InwardE =Tangent F = Radial OutwardIn parts (g)-(h), select which of Newton’s 3 laws or the 2 Conservation laws that best describes the situation.(g) A car accelerating up to 55 mph.A = Newton’s 1stB = Newton’s 2ndC = Newton’s 3rdD = Momentum E =Energy F = None of these(h) The forces acting on your head as it lays on your pillow while you sleep.A = Newton’s 1stB = Newton’s 2ndC = Newton’s 3rdD = Momentum E =Energy F = None of theseIn parts (i)-(j), select the best answer for the situation described.(i) Two 1.00 kg toys smash head on into each other totally inelastically. If one toy is moving at 12.0 m/s and theother is moving at –11.0 m/s, then the wreck moves at _______________. m1v1 - m2v2 = (m1 + m2) V+12.0kg·m/s - 11.0kg·m/s = +1.00kg·m/s ; +1.00kg·m/s ÷ 2.00kg = +0.500m/sA = –0.500 m/s B = –1.00 m/s C = 0 m/sD = +0.500 m/s E = +1.00 m/s F = None of these(j) Two 1.00 kg toys bounce off each other totally elastically. If one toy was moving at 1.00 m/s and the otherwas moving at –1.00 m/s, then the simple solution for the first toy is that afterward it moves at ___________.Have to conserve both momentum and K.E., so since identical, they just bounce the other way.Recall the Executive Time Waster Toy.A = –0.500 m/s B = –1.00 m/s C = 0 m/sD = +0.500 m/s E = +1.00 m/s F = None of thesed " # $ % &! " # $ h &! e # $ % &! " f $ % &! e # $ % &! e # $ % &! e # $ % &d " # $ % &! " # g % &! e # $ % &Physics 107 / Exam 2 [Form-A] Summer I 2007 Page 3The 2007 America’s Cup Sailboat Race – The Louis Vuitton Cup Round (35,000 points)2.) Right now, off the coast of Spain, very expensive sailboats are competing in aregatta to determine who will race against the Swiss boat Alinghi for theAmerica’s Cup in a few weeks. (a) The Italian boat ITA-94 Luna Rossa, m =22,400 kg, starts off from the line at rest and in the first few moments, acceleratesat ax = 4.00 m/s². Find the force F1 of the wind pushing on the sails making theboat go.Fma kg ms N1222 400 4 00 89 600== =,./,bgch(b) It takes 40 seconds for the boat to get up to its top speed. During that time the boat travelsa distance of 160. meters. Find the work done by the force F1 of the wind. If you did not getan answer to (a), use a force of 105,000 N.WFd N m J== =89 600 160 14 336 000,.,,bgbg(c) Once the boat has reached its top speed of 5.59 m/s (12.5 mph), the boat no longer accelerates even thoughthe wind is still pushing on the sails. Give the vector force Fdrag due to the hydrodynamic drag (waterresistance) of the boat sliding through the water.Assume boat is traveling in the +x direction.Now apply Newton’s 1st Law.FFFFF NFNxdragdragdragå=- ====°11089 60089 600 180,,@r(d) Find the Kinetic Energy of the boat at its top speed of 5.59 m/s (12.5 mph).KE mv kg m sJ===12212222 400 5 59350 000,./,bgbg(e) At a speed of 5.59 m/s (12.5 mph), the boat makes a sharp turn in the water of radius r = 40.0 meters. Findthe magnitude of the centripetal acceleration ac and the centripetal force Fc .avrmsmmsc===22255940 007812./../bgFma kg msNcc===22 400 0 781217 5002,./,bgchPhysics 107 / Exam 2 [Form-A] Summer I 2007 Page 4“Bad Boys, Bad Boys, Whatcha Gonna Do When, They Come for You…” COPS (35,000 points)3.) (a) A criminal races in a car of m = 2110 kg along the highway at 88 mph (39.3 m/s). A police Tahoe SUV,m = 2580 kg, accelerates as fast as it can. Find the maximum force of friction, if the coefficients of frictionbetween rubber tires and the road are 0.910 and 0.610.Fwmg kg ms NFF NNNfs s N== = ====2580 9 81 25 3100 910 25 31023 0302bgchbgb g./ ,.,,,,maxm(b) Use the Work-Energy Theorem to find the distance d it takes for the police car to go from rest to 39.3 m/s.WKEFd KE KE KE mvdKEFmvFkgNmfi ff==-======D1221221222580 39 323 03086 51bgbg.,.(c) The fleeing car is going too fast and at 39.3 m/s it flies off the top of a smallhill. Use Conservation of Energy to find out how fast the car is going when itfalls back onto the road 2.40 meters below the top of the hill.hmhmgh mv mgh mvmgh mv mvgh v vvghvms m msms12112122122211212122211222211222240 0222 981 240 39339 89==+=++=+==+=+=.;./ . ././chbgb gPhysics 107 / Exam 2 [Form-A] Summer I 2007 Page 5(d) The police would like to try a PIT maneuver, where one of the police cars gets behind and just off to the sideof the fleeing car and then rams it, to try to make the driver lose control and slide to a stop. With whatacceleration would the car slide to a stop?The sliding car would be using kinetic friction.Fwmg kg ms NFF NNFmaaFmNkgmsNfk k N== = ======= =2110 9 81 20 7000 610 20 70012 63012 6302110598622bgchbgb g./ ,.,,,./,m(e) Unfortunately the next traffic light is red and the fleeing car, m = 2110 kg and driving at 39.3 m/s, slams intoa stopped car of mass 2220 kg. If they collide in a totally inelastic collision, what is the speed V of the wreck?ppmv mv m m Vmv m m VVmvmmkg m skg kgmsbefore after=+=+=+=+=+=11 2 2 1 211 1 211122110 39 32110 222019