Question

Q. Ajmal sitting in a passenger train which was travelling at 72 km/hr observes that an express train, travelling in the same direction, took 18 seconds to pass him. If the express train was 360 m long, find the speed of the express train.

• A.
  42 km/hr
• B.
  52 km/hr
• C.
  92 km/hr
• D.
  144 km/hr

Answer 1

The correct option is D

144 km/hr
Here, the relative speed of the express train will be calculated wrt the position of man as the train took 18 seconds to pass him.
Relative speed $=\frac{360}{18}=20$ m/s
Converting it in to Km/hr, $20\times \left(\frac{18}{5}\right)=72$ km/hr
Using the concept of relative speed,
speed of the express train $=72+72=144$ km/hr