Department of PhysicsUniversity of MarylandCollege Park, MarylandPHYSICS 121 Prof. S. J. GatesFall 2002 Exam II Nov. 8, 2002This is a closed book examination. Read the entire examination before you beginto work. Be sure to read each problem carefully. Any questions should be directed tothe proctors. ALL work should be written within the examination booklet provided.There is a fifty minute time limit. Show all of your work. Use the backs of pages ifnecessary or request an extra booklet. Be sure to complete the front page of the ex-amination booklet including your name and recitation section. Show all calculationsneeded to support your answers, where necessary.Section I. Multiple Choice QuestionsEach question in this section is worth eight (8) points. You should NOT takemore than two minutes per question. If you do, it is advisable to continue on to thenext question!(1.) A child rides on a merry-go-round that completes one revolution everyfour seconds. She sits at a radius of 4 m from the center of the ride.Her centripetal acceleration is; (a.) 9.87ms. (b.) 6.21ms. (c.) 3.14ms.(d.) none of the above.(2.) Two identical blocks (m = 5 kg) start from rest from different heightsand slide down a frictionless inclined plane that makes an angle of 30owith respect to the horizontal. At the bottom of the incline the speedof the first is measured to be 2msand the other’s speed is 6msat thebottom of the incline. The height of the first is; (a.) three times thatof the second. (b.) nine times that of the second. (c.) 15 times thatof the second. (d.) none of the above.(3.) Two masses (m1= 3 kg and m2= 27 kg) at rest have the same amountof work done on them by a force F . The final velocity of the first massis: (a.) the same as the final velocity of the second mass. (b.) is threetimes the final velocity of the second mass. (c.) is nine times the finalvelocity of the second mass. (d.) none of the above.(4.) A wheel with an initial angular velocity of 2πradsbegins to uniformlyaccelerate until its angular velocity reaches 4πrads. It completes threerevolutions during this period. It reaches an angular speed of 4 πradsafter; (a.) 3 s. (b.) 2 s. (c.) 1 s. (d.) none of the above.(5.) Two cars are headed directly toward each other. The first has a massof 2000 kg with a speed of 6msand the other has a mass of 4000 kgwith a speed of 3ms. A collision last 0.12 s and afterward they arestuck together. The power deliver to the first car was; (a.) 600,000Watts. (b.) 12,000 Watts. (c.) 36,000 Watts. (d.) none of the above.Section II. Analytical QuestionsProblem (1.)A massless empty bucket is being filled with water starting at t = 0. At thatsame instant, a force F = 36Ns3t3is applied to the bucket causing it to acceler-ate along the x-axis. While it accelerates, it continues to fill. The bucket canonly hold 16 kg when full.(a.) If the acceleration of the bucket is measured to be 9ms4t2, how longdoes it take to fill it? (10 points).Problem (2.)Before a collision, one ball of mass 10 kg is rolling in the positive x-directionwith a speed of 7ms. A second ball with a mass of 5 kg is rolling in the positivey-direction with a speed of 14ms. After the collision, the two stick together.(a.) What is the angle of motion for the two joined balls after the collision?(5 points).Problem (3.)The angular speed of the earth is about 2 × 10−7radsand the radius of itsorbit about the sun is 1.5 × 1011m. The radius of the orbit of the planetMercury is 5.8 × 1010(a.) What is the angular speed of the Mercury? (10 points)2Problem (4.)A toy car with wheels of diameter 8 cm rolls on a floor without slipping.(a.) If the car travel a distance of 120 cm in 10 s, what is the angularvelocity of its wheels? (10 points)Problem (5.)A 6 kg mass is sliding on an inclined plane with friction. The inclinemakes an angle of 25owith regard to the horizontal. After travelling10 m, it losses 2 J of energy. If its initial velocity was 15ms;(a.) How far does it travel before coming to rest? (5 points).(b.) How long does it take for the mass to stop? (5 points).Problem (6.)A pendulum consists of a 10 kg mass at the end of a 2.5 m long rigid bar.At the lowest point of the arc, the mass has a centripetal acceleration of20ms2.(a.) What was the height from which the mass began its swing? (10
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