Athletic competition

In a 400-meter athletic competition, a participant covers the distance 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:

$$\begin{gathered} s=vt \\ {s}_1=80\text{m} \\ {s}_2=240\text{m} \\ {s}_3=80\text{m} \\ {v}_1=10\text{m/s} \\ {v}_2=7.5\text{m/s} \\ {v}_3=10\text{m/s} \\ {t}_1=s_1/v_1=80/10=8\text{s} \\ {t}_2=s_2/v_2=240/7.5=32\text{s} \\ {t}_3=s_3/v_3=80/10=8\text{s} \\ v=\frac{s_1+s_2+s_3}{t_1+t_2+t_3}=\frac{80+240+80}{8+32+8}=\frac{25}{3}\text{m/s}=8.3333\text{m/s} \end{gathered}$$

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