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Unformatted text preview: (b) Since s is proportional to doubling increases s by a factor of 4; s therefore becomes 154 m. (c) The original kinetic energy was converted into thermal energy by the negative work of friction. Reflect: To stop the car friction must do negative work equal in magnitude to the initial kinetic energy of the car. 7.20. Set Up: For part (a), estimate that the average person weighs 150 lb, walks at approximately and jogs at roughly For part (b), estimate that the car weighs 4000 lb and has a speed of 60.0 mph. Finally, for part (c), the workenergy principle tells us that the amount of work done by gravity must equal the gain in kinetic energy: Estimating the persons height to be her shoulder height would be roughly or Solve: (a) (b) (c) The change in kinetic energy is where Note the positive sign is a result of the force, acting in the direction of motion and therefore doing positive work. Substituting, Reflect: While we estimated that the persons speed doubled by jogging, his kinetic energy increased by a factor of 4.While we estimated that the persons speed doubled by jogging, his kinetic energy increased by a factor of 4....
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 Spring '07
 Shoberg
 Energy, Friction, Kinetic Energy, Work, Thermal Energy

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