Question

A person $A$ is sitting in one train while another person $B$ is in the second train. The trains are moving with velocities $60m/s$ and $40m/s$, respectively, in the same direction. Then the velocity of $B$ relative to $A$ will be

• A. 100 m/s in the direction of trains
• B. 20 m/s in the direction of trains
• C. 100 m/s in the direction opposite to that of trains
• D. 20 m/s in the direction opposite to that of the trains

Answer 1

Answer: (D)

${\vec{v}}_A=60\hat{i},{\vec{v}}_B=40\hat{i}$

${\vec{v}}_{B/A}={\vec{v}}_B-{\vec{v}}_A=40\hat{i}-60\hat{i}=-20\hat{i}$

So direction is opposite to that of trains.