[ Motion problems ]

Find the speed and length of the train if it is known that it passes a stationary observer in 7 seconds and took 25 seconds to travel past a platform 378 meters long.

#
For 378 m, the train required $25-7=18$ seconds. Therefore, its speed is $378: 18=21$ m/s, and the length is $21 \cdot 7=147$ m.

## Answer

$21 \mathrm{~m} / \mathrm{s}, 147 \mathrm{~m}$.