Question

How much time will a 200m long train running at 15m/sec take to cross a bridge of length 355m?

Answer 1

Hint: To find the time required by the train to pass the bridge at a certain speed we first find the total distance/length that is the sum of the length of the train and the bridge and then divide it by the speed of the train traveling. Hence, the time required to pass the bridge formula is:

Formula used:
Time (in seconds) required to cross the station \[=\dfrac{Lengt{{h}_{Train}}+Lengt{{h}_{Bridge}}}{Spee{{d}_{Train}}}\]
where \[Lengt{{h}_{Train}}\] is the length of the train in meters, \[Lengt{{h}_{Bridge}}\] is the length of the bridge, and \[Spee{{d}_{Train}}\] is the speed of the train in meter per second.

Complete Step-by-step Solution
Now placing the values of the \[Lengt{{h}_{Train}}\], \[Lengt{{h}_{Bridge}}\] and \[Spee{{d}_{Train}}\] in the formula as given in the question we get:
Time(in seconds) required to cross the station \[=\dfrac{Lengt{{h}_{Train}}+Lengt{{h}_{Bridge}}}{Spee{{d}_{Train}}}\]
\[=\dfrac{200m+355m}{15m/\sec }\]
\[=37\sec \]

Hence, the time (in seconds) required to cross the station is \[37\sec \].

Note:
Students may go wrong during the distance portion where the distance of the bridge alone will not bring the time but we have to add the length of the train as well and both the lengths are added and not subtracted because when one object moving approaches or cross another object (stationary), the length of both the objects is added giving the total distance.