Question

A $150m$ long train is moving north at a speed of $20m/s$. A bird flying south at a speed of $5m/s$ crosses the train. What is the time taken by the bird to cross the train?

• A. $30s$
• B. $15s$
• C. $6s$
• D. $3s$

Answer 1

The correct option is C $6s$

Let,

velocity of train $\left(v_t\right)=-20m/s$

velocity of bird $\left(v_b\right)=5m/s$

separation at $t=0s=150m$

Then,

velocity of bird wrt train $\left(v_{b/t}\right)=v_b-v_t$

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

let t be the time taken to cross.

Then,

$t=\frac{150m}{v_{b/t}}=\frac{150m}{25m/s}=6s$

Option - C is correct.