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# CHAPTER 2 Problem 116

<span class="room-tag">Most important in an investigation of an airplane crash by the U.S. National Transportation Safety Board is the data stored on the airplane’s flight-data recorder, commonly called the “black box” in spite of its orange coloring and reflective tape. The recorder is engineered to withstand a crash with an average deceleration of magnitude 3400g during a time interval of 6.50 ms. In such a crash, if the recorder and airplane have zero speed at the end of that time interval, what is their speed at the beginning of the interval? </span>

<br/>

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

Because of an average deceleration of magnitude 3400g and a time interval of 6.50 m
\begin{aligned}
v_f=v_i+a_{avg} \times \Delta t=0+3400g\times 6.5\times 10^{-3}=22.1g
\end{aligned}
<br>

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