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A train 150m long travels at 54 km/h. How long will it take to cross a pole?
10 seconds
12 seconds
8 seconds
15 seconds
10 seconds
Use the conversion factor: multiply km/h by 5/18 to get m/s. Since 54 is a multiple of 18 (18 * 3 = 54), the speed is 3 * 5 = 15 m/s, making the division 150/15 very simple.
Length of train (distance to cover) = 150m, Speed of train = 54 km/h.
Time=SpeedDistanceтАЛ
Use the conversion factor: multiply km/h by 5/18 to get m/s. Since 54 is a multiple of 18 (18 * 3 = 54), the speed is 3 * 5 = 15 m/s, making the division 150/15 very simple.
Failing to convert km/h to m/s, which leads to dividing 150 by 54 directly and resulting in an incorrect answer.
Convert speed to m/s
To make units consistent, convert 54 km/h to m/s by multiplying with 5/18.
54├Ч185тАЛ=15┬аm/s
Apply time formula
Since the train is crossing a pole, the distance to be covered is equal to the length of the train.
Time=15┬аm/s150┬аmтАЛ
Final Calculation
Divide the distance by the speed to get the time in seconds.
Time=10┬аseconds
A is correct because the calculated time is 10 seconds.
This concept is foundational for 'Trains' and 'Boats and Streams' problems; always verify if the object being passed has length (e.g., bridge, platform) or is a point object (e.g., pole, man).
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