## 49. Math Puzzle 6/69

A train, with a distance of $240 \mathrm{~m}$ between the first and last axle, travels at a speed of $72 \frac{\mathrm{km}}{\mathrm{h}}$ over a $36 \mathrm{~m}$ long bridge.

How much time elapses from the moment the first axle of the train reaches the beginning of the bridge until the last axle leaves the end of the bridge?
Given were: length of the train between the first and last axle $l_{Z}=240 \mathrm{~m}$, length of the bridge $l_{B}=36 \mathrm{~m}$, and the speed of the train $v=72 \frac{\mathrm{km}}{\mathrm{h}}=20 \frac{\mathrm{m}}{\mathrm{s}}$.

With $t=\frac{s}{v}, s=l_{B}+l_{Z}=276 \mathrm{~m}$ we get $t=\frac{276 \mathrm{~m}}{20 \frac{\mathrm{m}}{\mathrm{s}}}=13.8 \mathrm{~s}$.