Two trains of equal length take 10 s and 20 s, respectively, to cross a pole. If these trains are moving in the same direction, then how long will they take to cross each other?
- A10 sec
- B15 sec
- C40 sec
- D30 sec
Solution & Step-by-step Explanation
Let the length of each train be L.
Speed of the first train, v
1
=
10
L
Speed of the second train, v
2
=
20
L
When moving in the same direction, their relative speed is the difference between their individual speeds:
v
relative
=v
1
−v
2
=
10
L
−
20
L
=
20
2L−L
=
20
L
To cross each other completely, the total distance to be covered is the sum of their lengths:
Total Distance=L+L=2L
The time taken to cross each other is:
Time=
v
relative
Total Distance
=
20
L
2L
=2×20=40 seconds
Speed of the first train, v
1
=
10
L
Speed of the second train, v
2
=
20
L
When moving in the same direction, their relative speed is the difference between their individual speeds:
v
relative
=v
1
−v
2
=
10
L
−
20
L
=
20
2L−L
=
20
L
To cross each other completely, the total distance to be covered is the sum of their lengths:
Total Distance=L+L=2L
The time taken to cross each other is:
Time=
v
relative
Total Distance
=
20
L
2L
=2×20=40 seconds