Question

. A 160 m long train is moving north at a

speed of 15 m/s. A bird flying south at a

speed of 5 m/s crosses the train. The time

taken by the bird to cross the train is

(a) 8 s (b) 11.2 s

(c) 15.8 s (d) 56 s​

Answer 1

if the frame of referance is taken w.r.t. bird

Answer 2

Answer: 8 s [ Opt. A ]

Step by step explanation:

Given:

Distance to be covered by the bird: 160 m

Speed of train: 15 m/s

Speed of bird: 5 m/s

To find: time taken by the bird to cross the train

Considering the train with respect to the bird:

Velocity of the bird: 5m/s

Velocity of train: -15 m/s [ As the train is moving in the opposite direction ]

So,

Velocity = 5 - (-15) = 20 m/s

As we have to calculate the time taken by the bird to cross the train,

Time = Distance/Speed

= 160/20

= 8 s

Thus, time taken by the bird to cross the train is 8 seconds [ Opt. a ]