Athletic competition

In a 400 meter athletic competition, a participant covers the distance as given below.
find the average speed?

first 80 meters 10 m/s
next 240 meters 7.5 m/s
last 80 meters 10 m/s

Correct answer:

v =  8.3333 m/s

Step-by-step explanation:

$$\begin{gathered} s=vt \\ {s}_1=80\text{ m } \\ {s}_2=240\text{ m } \\ {s}_3=80\text{ m } \\ {v}_1=10\text{ m/s } \\ {v}_2=7.5\text{ m/s } \\ {v}_3=10\text{ m/s } \\ {t}_1=s_1\mathrm{/}{v}_1=80\mathrm{/}10=8\text{ s } \\ {t}_2=s_2\mathrm{/}{v}_2=240\mathrm{/}7.5=32\text{ s } \\ {t}_3=s_3\mathrm{/}{v}_3=80\mathrm{/}10=8\text{ s } \\ v={\displaystyle \frac{s_1+s_2+s_3}{t_1+t_2+t_3}}={\displaystyle \frac{80+240+80}{8+32+8}}={\displaystyle \frac{25}{3}}=8.3333\text{ m/s} \end{gathered}$$

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