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PHY111 Exam 2 Evening Version Name: Part I: Multiple-Choice Questions. 10/25/00 MacIsaac Page 1 SID#: These questions are worth 3 points each, and will be scored by the partial-credit scheme (correct answer in one response = 3 pts, correct in 2 responses = 2 pts, correct in 3 = 1 pt). Please clearly mark your responses on this page. Choose the BEST answer. 1. A coin is stationary on a wooden board. One side of the board is slowly raised until the coin begins to slide down the incline. If the angle between the board and the horizontal is 33˚, what is the coefficient of static friction between the coin and the wooden surface? A. 0.54 B. 0.84 C. 0.65 D. 0.74 2. An elevator weighing 10,000 N is supported by a steel cable. Determine the tension in the cable when the elevator is accelerated upward at 3.0 m/s2. A. 7.0 x 103 N B. 10,000 N C. 111 x 104 N D. 1.3 x 104 N 3. A car traveling 20 m/s rounds an 80-m radius horizontal curve with the tires on the verge of slipping. How fast can this car round a second curve, of radius 320 m? Assume that the coefficient of friction stays constant. A. 40 m/s B. 30 m/s C. 80 m/s D. 50 m/s 4. A car of mass M is going around a banked curve ( = 7˚ with respect to the horizontal). In a free body diagram reflecting this situation which force component equals the centripetal force? A. Mg Sin B. Mg C. FN Cos D. FN Sin 5. In a galaxy far, far away, two planets (Zorg and Endor) orbit the same star. Planet Zorg orbits the star in 300 days (2.59 x107 seconds) at a radius of 1.3 x1011 m. Planet Endor orbits at a radius of 2.7x1011 m. How long is a year on Endor? A. 6.0 x 107 sec B. 5.2 x 1014 sec C. 7.75 x 107 sec D. 2.4 x 108 sec PHY111 Exam 2 Evening Version 10/25/00 MacIsaac Page 2 Part II: Short Answer Questions. These questions are worth 3 points each, and require both units and reasonably significant figures. Partial credit may be awarded for work shown. Choose the BEST answer. 6. Two forces are acting on a 5 kg block. F1 has a magnitude of 45 N and is pushes from 65 degrees above the negative x axis. F2 has a magnitude of 25 N and pushes towards the negative x axis (directly left). What is the resultant acceleration vector (size and direction)? 7. The gravitational acceleration gmoon on the moon is 1/6th of the g on earth. If an object weighs 98 N on the earth what is its mass on the moon? 8. Your younger brother (mass 20 kg) is sitting on a snow sled (weight 29.4 N). You push him on level ground with of force of 50 N, at an angle of 40˚above the x axis. The coefficient of kinetic friction between the sled and the snow is 0.10 What frictional force exists between the sled and the snow? 9. A food processor has been turned on, and the Frappe button has been pressed. A blade of length 0.055m makes one complete revolution in 0.008 seconds. What centripetal acceleration is the tip of the blade experiencing? 10. On Uranus, the value of surface gravity is 9.21 N/kg. The radius of Uranus is 2.51 x 107 m. What is the mass of Uranus? PHY111 Exam 2 Evening Version 10/25/00 Part III: Problem-Solving & Discussion Questions. MacIsaac Page 3 These questions are worth 5 points each, and all require a diagram and explanation in clear phrases or point form. Please answer them on these pages provided. Partial credit will be awarded. 11. A sign is suspended from the side of a building by a steel wire and steel pole as shown. The sign has a mass of 150 kg, and the mass of the pole, fittings and wire are negligible. a. Draw a free body diagram for the steel pole in this situation. b. What is the weight of the sign? c. What is the vertical component (only) of the tension in the wire? d. What is total wire tension T? e. What are the size and direction of the normal force applied to the pipe by the wall? 50 90 40 Joe's Health Food Eat Here and Get Natural Gas PHY111 Exam 2 10/25/00 M1 (23 kg) and M2 (15 kg) are connected by a pulley and string on an inclined plane with = 25˚ as shown. µ = 0.15 (a) Draw a free body diagram for this situation. Indicate your coordinate axes. (b) Write Newton's Second Law for x and y motions of this situation. MacIsaac Page 12. M1 M2 (c) Write an expression for the acceleration of this system, and solve it (find a). (d) Write an expression for the string tension, and solve it (find T). PHY111 Exam 2 10/25/00 MacIsaac Page 13. The motion of objects orbiting a planet (orbital mechanics) can be described and predicted by combining the relationships between uniform circular velocity, gravitational attraction and centripetal acceleration. a. Use these three relationships to derive two formulas, one for orbital velocity in terms of planetary mass and orbital radius, and the other describing the relationship between orbital period, radius and planetary mass. Show your work. Mars has two tiny moons named Phobos (foe-bus) and Deimos (dee-mos). Phobos has an orbital period of 7.7 hours and orbits at average radius 9,410 km. Deimos has an average orbital radius of 23,500 km. b. What is the orbital period of Deimos? c. What is the mass of Mars? The International Space Station (ISS) is currently being constructed in low Earth orbit at an altitude of 285 km. The Earth's average radius is 6,370 km. d. What is the orbital velocity of ISS? e. What is the orbital period of the ISS?