A train crosses a bridge of length 150 m in 7.5 seconds and a lamp post on the bridge in 2.5 seconds...
A train crosses a bridge of length 150 m in 7.5 seconds and a lamp post on the bridge in 2.5 seconds. What is the length of the train in metres?
Answer/Solution
75 m
Steps/Work
Let Length of Train = L
Case-1: Distance = 150+L (While crossing the bridge)
Time = 7.5 Seconds
i.e. Speed = Distance / Time = (150+L)/7.5
Case-2: Distance = L (While passing the lamp post)
Time = 2.5 Seconds
i.e. Speed = Distance / Time = (L)/2.5
But Since speed has to be same in both cases so
(150+L)/7.50 = (L)/2.5
i.e. 3L = L + 150
i.e. 2L = 150
i.e. L = 75
Answer: option B
Case-1: Distance = 150+L (While crossing the bridge)
Time = 7.5 Seconds
i.e. Speed = Distance / Time = (150+L)/7.5
Case-2: Distance = L (While passing the lamp post)
Time = 2.5 Seconds
i.e. Speed = Distance / Time = (L)/2.5
But Since speed has to be same in both cases so
(150+L)/7.50 = (L)/2.5
i.e. 3L = L + 150
i.e. 2L = 150
i.e. L = 75
Answer: option B