Chapter 10 Skill Building

# Chapter 10 Skill Building - MasteringPhysics: Assignment...

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MasteringPhysics: Assignment Print View PSS 10.1: College Bored Learning Goal: To practice Problem-Solving Strategy 10.1 for problems involving conservation of mechancial energy. A bored college student decides to try bungee jumping. He attaches an elastic bungee cord to his ankles and happily jumps off a tall bridge across a river. He ends up barely touching the water before the cord jerks him back up. What is the mass of the student? The length of the relaxed cord is ; the distance from the bridge to the river surface is (where ), and the spring constant of the elastic cord is . MODEL: Choose a system without friction or other losses of mechanical energy. VISUALIZE: Draw a before-and-after pictorial representation. Define symbols that will be used in this problem, list known values, and identify what you're trying to find. SOLVE: The mathematical representation is based on the law of conservation of mechanical energy: . ASSESS: Check that your result has the correct units, is reasonable, and answers the question. Start by making simplifying assumptions appropriate for the situation. Part A Which objects are reasonable to include in the system in this problem? A. the bridge B. the student C. the bungee cord D. the air E. the river F. the planet earth G. the moon H. the sun Type alphabetically the letters corresponding to the correct answers. Do not use commas. For instance, if you think objects A and B should be included as part of the system, type AB .

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MasteringPhysics: Assignment Print View ANSWER: BCF The earth should indeed be included since the gravitational potential energy that we attribute to the student is, in fact, the energy associated with the gravitational interaction between the student and the earth; this energy, strictly speaking, belongs to the system "student-earth" rather than to the student alone. Part B Which assumptions are reasonable to make in this problem? A. The student can be treated as a particle moving with constant speed. B. The student can be treated as a particle moving with constant acceleration. C. The student cannot be treated as a particle. D. The air resistance is substantial. E. The air resistance is negligible. F. The amount of heat generated in the bungee cord is substantial. G. The amount of heat generated in the bungee cord is negligible. H. The bungee cord applies a constant (or zero) force on the student. I. The bungee cord can be modeled as a spring that obeys Hooke's law. Type alphabetically the letters corresponding to the correct answers. Do not use commas. For instance, if A and B are the only reasonable assumptions, enter AB . ANSWER: EGI The assumptions that air resistance is negligible and that there is essentially no heat generated in the bungee cord are important. Air resistance and the friction that generates heat are both nonconservative forces. If they were present, you would not be able to apply conservation of mechanical energy.
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## This homework help was uploaded on 04/08/2008 for the course PEP 111 taught by Professor Whittaker during the Fall '07 term at Stevens.

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Chapter 10 Skill Building - MasteringPhysics: Assignment...

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