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?
10
12
15
20
Explanation:
| Speed of the first train =$ \left(\dfrac{120}{10} \right) $m/sec = 12 m/sec. |
| Speed of the second train =$ \left(\dfrac{120}{15} \right) $m/sec = 8 m/sec. |
Relative speed = (12 + 8) = 20 m/sec.
| $\therefore $Required time =[$ \dfrac{(120 + 120)}{20}] $sec = 12 sec. |