Department of PhysicsUniversity of MarylandCollege Park, MarylandPHYSICS 121 Prof. S. J. GatesFall 2002 Practice 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.) Two teenagers decide to go sledding down a snow covered hillside. Onestarts at a height that is four times that of the other. The speed thatone reaches at the bottom of the hill is: (a.) the same as the speed ofthe other at the bottom of the hill. (b.) twice the speed of the other atthe bottom of the hill. (c.) four times the speed of the other at the bot-tom of the hill. (d.) none of the above.(2.) The power delivered by the force of gravity to an object moving five me-ters along the x-axis is; (a.) smaller than that for an object moving fivemeters along the y-axis. (b.) the same as that for an object moving fivemeters along the y-axis. (c.) larger than that for an object moving fivemeters along the y-axis. (d.) none of the above.(3.) Two forces F1and F2cause the same impulse when acting on a mass of20 kg. The force F1acts for 3s and F2acts for 9s. It must be the casethat; (a.) F1= F2. (b.) 3F1= F2. (c.) F1= 3F2. (d.) none of the above.(4.) A wheel starts from rest, accelerates uniformly until it completes ninerevolutions after 3 s. It reaches an angular speed of 4 πrads2after; (a.)9 s. (b.) 6 s. (c.) 3 s. (d.) none of the above.(5.) Two cars are headed directly toward each other. One has a mass of2000 kg with a speed of 6msand the other has a mass of 4000 kgwith a speed of 3ms. After the collision they are stuck together andmove with a speed of; (a.) 0ms. (b.) 3ms. (c.) 6ms(d.) none of theabove.Section II. Analytical QuestionsProblem (1.)Before a collision, one ball of mass 10 kg is rolling in the positive x-directionwith a speed of 7ms. A second ball of identical mass is rolling in the positivey-direction with an unknown speed. After the collision, the two stick togetherand are observed to move along a line that makes a 45oangle with respect tothe x-axis.(a.) What is the unknown speed of the second ball before the collision?(10 points).Problem (2.)The space shuttle is in orbit around the earth at a altitude of 5100 km. It firesits rocket motors to reach a higher orbit. When it does, the astronauts on-boarddiscover that it takes the twice as long to complete one orbit around the earth.(a.) What is altitude of the new orbit of the space shuttle? (10 points)Problem (3.)The power at time t delivered to a ball is given by P =Js14t13. The accelera-tion of the ball at time t is given by a =ms9t7and the velocity of the ball attime t is v = 7ms7t6.(a.) What is the mass of the ball? (10 points).2Problem (4.)If a 5 kg mass at the end of a pendulum 5 m long is released from rest 4 mabove its lowest point, what is its centripetal acceleration when it reaches3 m above its above its lowest point? (10 points).Problem (5.)Two football linemen on opposite teams are waiting for the quarterback toget the snap f rom the center. The first lineman has a weight of 250 N andwhen he collides with his opponent travels at a speed of 1.5ms. The secondlineman has a weight of only 225 N but he is quicker.(a.) How fast must the second lineman be travelling so that after theimpact neither one “wins? ” (10 points)Problem (6.)A 6 kg mass is sliding on a surface with friction. After travelling 10 m, itlosses 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
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