3.52 A passenger on a train knows that the speed of this train on this section of the track is 40 km/h. As soon as a passing train started to go by the window, the passenger started a stopwatch and noticed that the passing train went by the window for 3 seconds. Determine the speed of the passing train, given that its length is 75 m.

## Work

## Paбoma

## Work
3.52 Instruction. The condition of the problem is equivalent to the oncoming train standing still, while the passenger rushes past it at a speed equal to $(v+40)$ km/h, where $v$ is the sought speed.

Answer: $50 \mathrm{km} / \mathrm{h}$.