Question 58

A moving train passes a platform 50m long in 14 seconds and a lamp post in 10 seconds. The speed of the train (in km/h) is :

Solution

Let the speed of train = $$s$$ m/sec and length of train = $$l$$ m

Using, time = distance/speed

The train passes a lamp post in 10 seconds

=> $$10=\frac{l}{s}$$

=> $$l=10s$$ --------(i)

Similarly, $$14=\frac{50+l}{s}$$

=> $$14s=50+10s$$ [Using (i)]

=> $$14s-10s=4s=50$$

=> $$s=\frac{50}{4}=12.5$$ m/sec

$$\therefore$$ Speed of train (in km/hr) = $$\frac{18}{5} \times 12.5=45$$ km/hr

=> Ans - (D)

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