A train runs across a post in 15 seconds and across a platform of length 100m in 25 seconds. Determine the length of this train:
Answer: D
Let us assume for this question that the length of train is x metres and it is assumed to be running at the speed of y m/sec.
A pole is assumed as a point object.
=>Time taken by the train to pass the pole= x/y
=>15=x/y
=>y=x/15
Now, the train passes the platform which is 100 m in length in 25 seconds.
=>x+100/y=25
=>x+100/25=y
Equating speed generated from both cases:
x+100/25=x/15
Therefore x = 150 metres.