Discussion Forum

Two trains of equal lengths take 10 seconds and 15 seconds respectively to cross a telegraph post. If the length of each train be 120 metres, in what time (in seconds) will they cross each other travelling in opposite direction ?

Answer:

Explanation:

Speed of the first train $=\left(\frac{120}{10}\right)$ m/sec $=12$ m/sec.

Speed of the second train $=\left(\frac{120}{15}\right)$ m/sec $=8$ m/sec.

Relative speed $=(12+8)$ m/sec $=20$ m/sec.

$\therefore$ Required time $=\frac{(120+120)}{20}$ sec = 12 sec.