Question

(C) 4 ms
Two trains each travelling with a speed of
37.5 km/h are approaching each other on the
same straight track. A bird that can fly at 60
km/h flies off from one train when they are 90
km apart and heads directly for the other train.
On reaching the other train it flies back to the
first and so forth. Total distance travelled by
the bird is
(1
Arm
621-m
d7 1m​

Answer 1

The answer has 2 parts:

1) The time taken by trains to meet each other

The relative velocity : 37.5 +37.5 =75 Km/hr (since they are travelling towards each other)

The distance between them : 90 Km

So the time taken by trains to meet each other is 90km/(75km/hr)= 1.2hr= 72 mins

2) Speed of the bird is 60Km/hr

So basically the bird can only travel till the trains meet each other, in other words the bird has 72 mins to travel

so the distance travelled by bird is (60km/hr)X(72/60)= 72 Kms.