Question

What is the speed of the bullet train?

I. The train crosses a lamp post in 26 seconds.

II. The train crosses a platform of length 500 metres in 54 seconds.

III. The train crosses another train running in the same direction in 64 seconds.

• A. I and II only
• B. II and III only
• C. I and III only
• D. Any two of the three
• E. None of these

Answer 1

The correct option is A

I and II only

Let the speed of the train be `x' m/sec.

Time taken to cross a lamp post $=\frac{Lengthofthetrain}{Speedofthetrain}$

Time taken to cross a platform = $=\frac{\left(Lengthoftrain+Lengthofplatform\right)}{Speedofthetrain}....\left(ii\right)$

$Igives,26=\frac{l}{x}\Rightarrow l=26xIIgives,54=\frac{l+500}{x}\Rightarrow \frac{26x+500}{x}=54\Rightarrow x=\frac{125}{7}m/sec.$

Thus I and II give the speed of the train.