• # question_answer Two trains of equal length take 10 seconds and 15 seconds respectively to cross a telegraph post. If the length of each train be 120 m, in what time (in seconds) will they cross each other travelling in opposite directions? A)  12 sec  B)  8 sec C)  11 sec  D)  15 sec

[a] Speed of first train $=\frac{120}{10}=12\,m/s$ Speed of second train $=\frac{120}{15}=8m/s$ $\therefore$ $t=\frac{120+120}{12+8}=\frac{240}{20}=12\,sec$