Question

A $120\, m$ long train is moving towards west with a speed of $10\, m / s$. A bird flying towards east with a speed of $3\, m / s$ crosses the train. The time taken by the bird to cross the train will be :

• A. 16 sec
• B. 12 sec
• C. 10 sec
• D. 8 sec

Answer 1

Answer: (D)

8 sec

Answer 2

Here : Length of train $l=120\, m$ Speed of train $v_{\text {train }}=10\, m / s$ towards west Speed of bird $v_{\text {bird }}=5\, m / s$ towards east The relative velocity of bird with respect to the train $v=v_{\text {train}}+v_{\text {bird }}=10+5=15\, m / s$ Hence, time taken to cross the train is $=\frac{s}{v}=\frac{120}{15}=8\, \sec$