44_Physics ProblemsTechnical Physics

44_Physics ProblemsTechnical Physics - Chapter 2*P2.59(a(b...

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Chapter 2 45 *P2.59 (a) As we see from the graph, from about 50 s to 50 s Acela is cruising at a constant positive velocity in the + x direction. From 50 s to 200 s, Acela accelerates in the + x direction reaching a top speed of about 170 mi/h. Around 200 s, the engineer applies the brakes, and the train, still traveling in the + x direction, slows down and then stops at 350 s. Just after 350 s, Acela reverses direction ( v becomes negative) and steadily gains speed in the x direction. t (s) 100 200 300 –100 100 200 400 v t –50 0 0 FIG. P2.59(a) (b) The peak acceleration between 45 and 170 mi/h is given by the slope of the steepest tangent to the v versus t curve in this interval. From the tangent line shown, we find a v t == = () slope mi h s mi h s m s 2 155 45 100 50 22 098 .. af . (c) Let us use the fact that the area under the
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