Q. A $210\ m$ long train is moving due North at a speed of $25\ m/s$. A small bird is flying due South a little above the train with speed $5\ m/s$. The time taken by the bird to cross the train is
A) $6s$
B) $7s$
C) $9s$
D) $10s$
Explanation
(b) Relative velocity of bird $w.r.t.$ train $= 25 + 5 = 30\ m/s$
Time taken by the bird to cross the train $t = \frac{210}{30} = 7\ sec$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.