1.1 Misha noticed that a tram passed by him in 3 seconds, and a tunnel 100 meters long in 13 seconds. Find the speed of the tram (in meters per second), assuming that it remains the same throughout the entire observation period.
Solution. Let the speed of the tram (in meters per second) be $v$, and the length of the tram (in meters) be $l$. If $t_{1}$ and $t_{2}$ are the times it takes for the tram to pass by Mishka and through a tunnel of length $a$ respectively, then

$$
\left\{\begin{array} { l } 
{ l = v \cdot t _ { 1 } } \\
{ a + l = v \cdot t _ { 2 } }
\end{array} \Longrightarrow \left\{\begin{array}{l}
v=\frac{a}{t_{2}-t_{1}} \\
l=\frac{a t_{1}}{t_{2}-t_{1}}
\end{array}\right.\right.
$$

Since $t_{1}=3, t_{2}=13$ and $a=100$, then $v=10$.

Answer: 10. (A)

![](https://cdn.mathpix.com/cropped/2024_05_06_997c53c06135e2de9c16g-01.jpg?height=64&width=727&top_left_y=1367&top_left_x=716)