College Physics (7th Edition)

Published by Pearson
ISBN 10: 0-32160-183-1
ISBN 13: 978-0-32160-183-4

Chapter 2 - Kinematics: Description of Motion - Learning Path Questions and Exercises - Exercises - Page 66: 84

Answer

(a) Graph (b) $a=3.67\,\mathrm{m/s^2}$ (c) $77\,\mathrm{m}$ and $167\,\mathrm{m}$ (d) $v=36.76\,\mathrm{m/s}$

Work Step by Step

(a) Take a look at the graph. (b) To compute the acceleration of car A, we consider the refrence frame of car B. Then car A will appear to start accelerating from rest, $v_0=0$, for a total time of $t=7.00\,\mathrm{s}$ and covers a displacement of $\Delta x=50.0+40.0=90.0\,\mathrm{m}$. Using the kinematic equation, \begin{align*} \Delta x&=v_0t+{1\over 2}at^2\\ 90.0&=0+{1\over 2}a(7.00)^2\\ a&={180\over 49.0}\\ a&=3.67\,\mathrm{m/s^2} \end{align*} Acceleration is independent of which inertial frame the observation is made. Hence the acceleration of car A will be the same even from the ground frame: $3.67\,\mathrm{m/s^2}$. (c) Car B travels with a constant speed throughout, hence the distance covere by it simply, $$\Delta x=v\Delta t=11\times 7.00=77\,\mathrm{m}$$ The total distance covered by Car A can be computed from the kinematic equation: \begin{align*} \Delta x&= v_0t+{1\over 2}at^2\\ &=(11)(7.00)+{1\over 2} (3.67)(7.00)^2\\ &=77+89.9\\ &=167\,\mathrm{m} \end{align*} (d) Car accelerated throughout the passing and hence its speed will have increased. To find the speed at the end of the procedure, we use the kinematic equation: \begin{align*} v^2&=v_0^2+2a\Delta x\\ &=11^2+2(3.67)(167)\\ &=121+1230\\ &=1351\\ v&=\sqrt{1351}\\ v&=36.76\,\mathrm{m/s} \end{align*}
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