p02_031

Fundamentals of Physics,Vol 1 (Chapters 1 - 20)

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31. We choose the positive direction to be that of the initial velocity of the car (implying that a< 0 since it is slowing down). We assume the acceleration is constant and use Table 2-1. (a) Substituting v 0 = 137 km / h=38 . 1m / s, v =90km / h=25m / s, and a = 5 . 2m / s 2 into v = v 0 + at , we obtain t = 25 m / s 38 m / s 5 . / s 2 =2 . 5s . (b) Wetakethecartobeat x = 0 when the brakes are applied (at time t = 0). Thus, the coordinate of the car as a function of time is given by x = (38) t + 1 2 ( 5 . 2) t 2 in SI units. This function
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