Question

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

• A. 10
• B. 12
• C. 15
• D. 20

Answer 1

The correct option is B 12

For first train

Distance covered$=120m$

Time taken$=10sec$

Speed of the first train$=\frac{Distance}{Time}=\frac{120}{10}=12m/sec$

For second train

Distance covered$=120m$

Time taken$=15sec$

Speed of the first train$=\frac{Distance}{Time}=\frac{120}{15}=8m/sec$

=(12010)m/sec=12m/sec=(12015)m/sec=8m/secRelative speed $=(12+8)=20m/sec$

Total distance$=120+120=240m$

Time (in seconds) in which they cross each other travelling in opposite direction$=\frac{\text{Total distance}}{\text{Relative speed}}=\frac{240}{20}=12sec$

Hence the correct option is (B).