5. Two cars are driving towards a single intersection on two mutually perpendicular roads at constant speeds. At the initial moment, the first car was at a distance of $s_{1}=1600$ m from the intersection, and for the second car, the analogous distance was $s_{2}=800 \mathrm{M}$. The speed of the first car is $v_{1}=72 \mathrm{~km} / \mathrm{q}$. At the moment when the first car reached the intersection, the distance between the cars was $s=200$. . Determine the speed of the second car. (15 points)
Answer: 7.5 m/s or $12.5 \mathrm{~m} / \mathrm{s}$

## Solution.

The time of the first car's movement to the intersection $t_{1}=\frac{S_{1}}{v_{1}}=\frac{1600}{20}=80 \mathrm{s}$

There are two possible scenarios. The second car has already passed the intersection or has not yet reached it. Therefore, the distance it has traveled:

$l_{1}=s_{2}-s=800-200=600 \mathrm{m}$ (3 points) or $l_{2}=s_{2}+s=800+200=1000 \mathrm{m}$

As a result, the speed of the second car $v_{2}=\frac{l_{1}}{t_{1}}=\frac{600}{80}=7.5 \mathrm{m} / \mathrm{s}$

or $v_{2}=\frac{l_{2}}{t_{1}}=\frac{1000}{80}=12.5 \mathrm{~m} / \mathrm{s} \quad(3$ points $)$