A 150 m long train is travelling from West to East at a speed of 20 m/s. A bird is flying from East to West at a speed of 5 m/s above the train. How long will the bird take to cross the train ?

Question

\[(a)\;6s \quad (b)\;7.5s \quad (c)\;10s \quad (d)\;30s\]

Answer 1

Relative velocity of bird with respect to train

$=5-(-20)=25m/s$

Time taken by train $=\large\frac{150}{25}$$=6s$

$v_b=v_{\large bird}=5 m/s;\quad v_T=v_{\large train}=-20 m/s$

Relative velocity of bird with respect to train

$=v_b-v_T$

$=5-(-20)$

$=25 m/s$

The bird take 6s to cross the train

Hence a is the correct answer.