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A train 150m long is running at a speed of 54 km/h. How much time will it take to cross a pole?
8 seconds
10 seconds
12 seconds
15 seconds
10 seconds
Use the conversion factor: speed in km/h multiplied by 5/18 gives speed in m/s. 54 * (5/18) = 15 m/s. Then, distance 150 / 15 = 10.
Length of the train (distance to be covered) = 150m, Speed of the train = 54 km/h.
Time=SpeedDistanceтАЛ
Use the conversion factor: speed in km/h multiplied by 5/18 gives speed in m/s. 54 * (5/18) = 15 m/s. Then, distance 150 / 15 = 10.
Failing to convert the speed from km/h to m/s, which leads to an incorrect answer as units must be consistent (meters and seconds).
Convert speed to m/s
To maintain uniform units, convert 54 km/h to m/s using the conversion factor 5/18.
54├Ч185тАЛ=15┬аm/s
Define distance
When a train crosses a pole, the total distance covered is equal to the length of the train itself.
Distance=150┬аm
Calculate time
Apply the time formula using the converted speed and the train length.
Time=15150тАЛ=10┬аseconds
B is correct because the calculation of 150 meters divided by 15 m/s results in exactly 10 seconds.
This concept of distance and speed is foundational for problems on 'Trains crossing platforms', where the total distance becomes 'Length of train + Length of platform'.
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