Two trains cross each other in seconds when running in opposite directions along parallel tracks. The faster train is m long and crosses a lamp post in seconds. If the speed of the other train is km/hr less than the faster one, its length, in m, is
Two trains cross each other in seconds when running in opposite directions along parallel tracks. The faster train is m long and crosses a lamp post in seconds. If the speed of the other train is km/hr less than the faster one, its length, in m, is
Solution
Let's solve this step-by-step, breaking down this relative speed problem into manageable parts.
The faster train crosses a lamp post in 12 seconds. When a train crosses a lamp post, it travels a distance equal to its own length.
Speed of faster train =
We're told the slower train's speed is 6 km/hr less than the faster train. Since we're working in m/s, let's convert this difference:
To convert km/hr to m/s, we multiply by
This is because:
Speed difference =
Speed of slower train =
When two objects move in opposite directions, their relative speed is the sum of their individual speeds.
Relative speed =
When two trains cross each other, the total distance covered equals the sum of their lengths.
Using the formula: Distance = Speed × Time
Total distance = Relative speed × Time =
Sum of lengths of both trains = 350 m
Length of second train = Total length - Length of first train
Length of second train =
We remember this approach for similar problems: We find individual speeds using given information, calculate relative speed by adding for opposite directions or subtracting for same direction, use relative speed × time = sum of lengths, and solve for the unknown length.
Answer: 190 m