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A train 150m long is running at 54 km/hr. How long will it take to cross a pole?
10 ┬аseconds
12 ┬аseconds
8 ┬аseconds
15 ┬аseconds
10 ┬аseconds
Use the conversion factor: multiply km/hr by 5/18 to get m/s. Then, simply divide the length (150) by the speed (15) to get 10 seconds.
Length of the train (d) = 150m, Speed of the train (v) = 54 km/hr.
t=vdтАЛ
Use the conversion factor: multiply km/hr by 5/18 to get m/s. Then, simply divide the length (150) by the speed (15) to get 10 seconds.
The most common mistake is forgetting to convert km/hr to m/s, which leads to using 54 instead of 15 as the speed in the denominator.
Convert speed to m/s
To maintain units consistency (meters and seconds), convert speed from km/hr to m/s by multiplying by 5/18.
v=54├Ч185тАЛ=3├Ч5=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 itself (150┬аm).
t=SpeedDistanceтАЛ=15150тАЛ
Final calculation
Dividing the distance by the speed gives the total time taken to cross the pole.
t=10┬аseconds
A is correct because the train covers 150 meters at 15 meters per second, resulting in exactly 10 seconds.
This concept is foundational for 'Trains' problems. Always remember that crossing a pole, tree, or signal means the train covers its own length; crossing a platform or bridge means it covers length of train + length of object.
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