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A train 150m long is running at a speed of 54 km/hr. How long will it take to pass a pole?
8 ┬аseconds
10 ┬аseconds
12 ┬аseconds
15 ┬аseconds
10 ┬аseconds
Multiply the speed by 185тАЛ mentally to convert km/hr to m/s. Here, 54├Ч185тАЛ=3├Ч5=15 m/s, then divide distance 150m by 15 m/s.
Train length (distance) = 150m, Speed = 54 km/hr
t=sdтАЛ
Multiply the speed by 185тАЛ mentally to convert km/hr to m/s. Here, 54├Ч185тАЛ=3├Ч5=15 m/s, then divide distance 150m by 15 m/s.
Forgetting to convert the speed from km/hr to m/s, which results in an incorrect answer like 2.77 seconds.
Convert speed to m/s
To ensure units are consistent, convert 54 km/hr to m/s by multiplying with 185тАЛ.
v=54├Ч185тАЛ=15┬аm/s
Identify distance
When a train passes a pole, the total distance covered is equal to the length of the train.
d=150┬аm
Calculate time
Using the formula t=vdтАЛ, divide the train length by the speed in m/s.
t=15150тАЛ=10┬аseconds
B is correct because the train covers its own length of 150m at a converted speed of 15 m/s, resulting in exactly 10 seconds.
This concept of distance over speed is foundational for solving problems related to trains crossing platforms or tunnels, where the total distance becomes LtrainтАЛ+LobjectтАЛ.
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