211_Physics ProblemsTechnical Physics

211_Physics ProblemsTechnical Physics - Chapter 7*P7.68 P=...

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Chapter 7 213 *P7.68 P = 1 2 23 Dr v ρπ (a) a == × 1 2 1 1 20 1 5 8 2 17 10 2 3 3 .. . kg m m m s W 3 ej af bg π (b) b a b a v v F H G I K J 3 3 3 3 24 8 32 7 ms b =×= × 27 2 17 10 5 86 10 34 W W P7.69 (a) The suggested equation tb w d = implies all of the following cases: (1) w d = F H G I K J 2 2 (2) t b w d 22 F H G I K J = F H G I K J (3) t bw d F H G I K J = F H G I K J and (4) F H G I K J = F H G I K J w d These are all of the proportionalities Aristotle lists. F f k = µ k n n w d v = constant FIG. P7.69 (b) For one example, consider a horizontal force F pushing an object of weight w at constant velocity across a horizontal floor with which the object has coefficient of friction k . Fa = m implies that: +− = nw 0 and Fn k −= 0 so that Fw k = As the object moves a distance d , the agent exerting the force does work WF d F d w d k ° = cos cos θµ 0 and puts out power = W t This yields the equation tw d k = which represents Aristotle’s theory with
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