07_InstSolManual_PDF_Part4 - 7-4 Chapter 7(c The normal...

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(c) The normal force, n , is perpendicular to the displacement and thus does zero work. Reflect: Friction does positive work and gravity does negative work. The net work done is zero. 7.12. Set Up: Use to calculate where K is equal to the change in thermal energy. Solve: (a) (b) Reflect: When the mass increases by a factor of two, the speed required decreases by a factor of 7.13. Set Up: Use and solve for m . Solve: Reflect: The kinetic energy of an object is proportional to the mass of the object. 7.14. Set Up: Use to relate and K . Solve: (a) (b) K is proportional to so K increases by a factor of 4 when doubles. 7.15. Set Up: Use to relate and K . Let and be speed and kinetic energy when Solve: (a) and so (b) Since we obtain This means that the decrease in K is 7.16. Set Up: Applying to relate and K results in Solve: (a) where and Substituting, (b) Now let and Substituting, Reflect: When K changes by a factor of two, the speed changes by a factor of When changes by a factor of two, the kinetic energy changes by a factor of 7.17.
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