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# CHAPTER 2 Problem 109

<span class="room-tag">An automobile driver increases the speed at a constant rate from 25 km/h to 55 km/h in 0.50 min. A bicycle rider speeds up at a constant rate from rest to 30 km/h in 0.50 min. What are the magnitudes of (a) the driver’s acceleration and (b) the rider’s acceleration?</span>

<br/>

根據平均加速度之定義：
\begin{aligned}
a_{avg} ={\Delta v \over {\Delta t}}=\frac{v_f-v_i}{\Delta t}
\end{aligned}
<br>

(a)
\begin{aligned}
a_{avg} ={\Delta v \over {\Delta t}}=\frac{v_f-v_i}{\Delta t}=\frac{(55-25) \ \mathrm{km/h}}{0.5 \ \mathrm{min}}=\frac{30 \times \frac{1000 \ \mathrm{m}}{3600 \ \mathrm{s}}}{30 \ \mathrm{s}} \approx 0.28 \ (\mathrm{m/s}^2)
\end{aligned}

(b)
\begin{aligned}
a_{avg} ={\Delta v \over {\Delta t}}=\frac{v_f-v_i}{\Delta t}=\frac{(30-0) \ \mathrm{km/h}}{0.5 \ \mathrm{min}}=\frac{30 \times \frac{1000 \ \mathrm{m}}{3600 \ \mathrm{s}}}{30 \ \mathrm{s}} \approx 0.28 \ (\mathrm{m/s}^2)
\end{aligned}
<br>

###### tag: `Fundamentals of Physics`