Download Coefficient of Rolling Friction - General Physics - Past Paper and more Exams Physics in PDF only on Docsity! First Name: ____________________ Last Name:_____________________ Section: ________ ■ 1 March 26, 2008 Physics 207 EXAM 2 Please print your name and section number (or TA’s name) clearly on all pages. Show all your work in the space immediately below each problem. Your final answer must be placed in the boxes provided. Problems will be graded on reasoning and intermediate steps as well as on the final answer. Be sure to include units wherever necessary, and the direction of vectors. Each problem is worth 20 points. Try to be neat! Check your answers to see that they have the correct dimensions (units) and are the right order of magnitude. You are allowed one sheet of notes (8.5” x 11”, 2 sides), a calculator, and the constants in this exam booklet. The exam lasts exactly 90 minutes. Constants: Acceleration due to gravity at the earth’s surface: g = 9.81 m/s2 SCORE: Problem 1: __________ Problem 2: __________ Problem 3: __________ Problem 4: __________ Problem 5: __________ TOTAL: ___________ Don't open the exam until you are instructed to start. “I have no special talent. I am only passionately curious.” A. Einstein First Name: ____________________ Last Name:_____________________ Section: ________ ■ 2 Problem 1 a.) A 1000 kg car climbs a 5.0° slope at a constant velocity of 80.0 km/h. Assuming that air resistance may be neglected, at what rate must the engine deliver energy to the drive wheels of the car? Express your answer in kW. (10 pts) b.) Truck brakes can fail if they get too hot. In some mountainous areas, ramps of loose gravel are constructed to stop runaway trucks that have lost their brakes. The combination of a slight upward slope and a large coefficient of rolling friction as the truck tires sink into the gravel brings the truck safely to a halt. Suppose a gravel ramp slopes upward at 6.0° and the coefficient of friction is 0.40. Find the length of a ramp that will stop a 15,000 kg truck that enters the ramp at 35 m/s (about 75 mph). (10 pts) First Name: ____________________ Last Name:_____________________ Section: ________ ■ 5 d.) What is the torque (magnitude and direction) on the flywheel? (4 pts) e.) Find the work done by the force on the flywheel (make sure to indicate whether the work is positive or negative) (4 pts.) First Name: ____________________ Last Name:_____________________ Section: ________ ■ 6 Problem 4 Timbie and Chung want to determine whose car is more massive. They are advised by Physics 207 students to find out the answer by colliding the cars together. In experiment 1, Timbie’s car, with mass mT, is at rest when Chung’s car, mC crashes into it with initial velocity vi. After the impact the two cars remain locked together and move with velocity vf. In experiment 2, the cars are pulled apart from each other and collided again, this time with Chung’s car at rest and Timbie’s crashing into it with the same initial velocity, vi, as in experiment 1. The cars remain locked together after the impact and this time move with velocity vf′. a.) In experiment 1, what is the ratio of the final kinetic energy to the initial kinetic energy? Express your answer in terms of mT and mC. (7 pts) b.) Using the results of both experiments, what is the mass of mT in terms of mC, vf, and vf′? (7pts) First Name: ____________________ Last Name:_____________________ Section: ________ ■ 7 Now for a different problem: c.) A 1.6 kg particle moving along the x-axis experiences the net force shown in the figure. The particle's velocity is 4.0 m/s in the positive x direction at x = 0 m. What is its velocity at x = 2 m? (6 pts)
