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title: CHAPTER 2 Problem 06
tags: [Fundamentals of Physics]

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# CHAPTER 2 Problem 06

<span class="room-tag">The 1992 world speed record for a bicycle (human-powered vehicle) was set by Chris Huber. His time through the measured 200 m stretch was a sizzling 6.509 s, at which he commented, “Cogito ergo zoom!” (I think, therefore I go fast!). In 2001, Sam Whittingham beat Huber’s record by 19.0 km/h. What was Whittingham’s time through the 200 m?</span>

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假設是Sam Whittingham的速度為平均速度，根據平均速度之定義：
\begin{aligned}
v_{avg} ={{\Delta x } \over {\Delta t}} \Longrightarrow \Delta t={{\Delta x } \over v_{avg}}
\end{aligned}

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將速度為 19.0 km/h 與位移(距離) 200m 代入：
\begin{aligned}
\Delta t={{\Delta x } \over v_{avg}}={200\text{m} \over {19 {km \over h}}}={200\text{m} \over {19 \times {1000m \over 3600s}}}=37.9 (\text{s})....(?)
\end{aligned}

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算出來的秒數出奇的長？於是我計算了Chris Huber的紀錄，速度大約是 110.62 km/h。所以 19.0 km/h 一點也不快！實際上，Sam Whittingham的紀錄在2009年有一個 133.68 km/h，這個數值比 19.0 km/h 合理多了！

如果是利用2009年的紀錄：133.68 km/h，可以得到 200 m的秒數約為
\begin{aligned}
\Delta t={{\Delta x } \over v_{avg}}={200\text{m} \over {133.68 {km \over h}}}={200\text{m} \over {133.68 \times {1000m \over 3600s}}}=5.38 (\text{s})
\end{aligned}

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