<style>
.room-tag {
background-color: #ffffff;
color: #000000;
display: inline-block;
padding: 1px 5px;
border-radius: 8px;
text-align:justify;
font-size:22px;
font-weight:600;
}
</style>

# CHAPTER 2 Problem 03

<span class="room-tag">An automobile travels on a straight road for 40 km at 30 km/h. It then continues in the same direction for another 40 km at 60 km/h.
a) What is the average velocity of the car during the full 80 km trip? (Assume that it moves in the positive x direction.)
b) What is the average speed?
c) Graph x versus t and indicate how the average velocity is found on the graph.</span>

<br/>

a)根據平均速度的定義
\begin{aligned}
v_{avg}={\Delta x \over \Delta t }
\end{aligned}

因此需要計算此過程的總時間，第一段時間為
\begin{aligned}
\Delta t_1={40 \over 30 }={4 \over 3}(\mathrm{H})
\end{aligned}

第二段時間為

\begin{aligned}
\Delta t_1={40 \over 60 }={4 \over 6}(\text{H})
\end{aligned}

故平均速度為
\begin{aligned}
v_{avg}={\Delta x \over \Delta t }={80 \over {{4 \over 3}+{4 \over 6}}}={{80\times 6} \over 12}= +40 \ (\text{km/H})\\(+號代表方向性)
\end{aligned}

b)根據平均速率的定義
\begin{aligned}
v_{avg}={L \over \Delta t }={80 \over {{4 \over 3}+{4 \over 6}}}={{80\times 6} \over 12}= 40 \ (\text{km/H})
\end{aligned}

c)

###### tags: `Fundamentals of Physics`