Question

Two trains are moving east ward with velocities $10{\text{ms}}^{-1}$ and $15{\text{ms}}^{-1}$ on parallel tracks. Calculate the relative velocity of slow train w.r.t. the fast train.

• A. $5{\text{ms}}^{-1}$ towards west.
• B. $5{\text{ms}}^{-1}$ towards east.
• C. $25{\text{ms}}^{-1}$ towards west.
• D. $25{\text{ms}}^{-1}$ towards east.

Answer 1

The correct option is A $5{\text{ms}}^{-1}$ towards west.

Velocity of slower train, $v_1=10{\text{ms}}^{-1}$
Velocity of faster train, $v_2=15{\text{ms}}^{-1}$
Relative velocity of slow train w.r.t. the fast train $v_{12}=v_1-v_2=10-15=-5{\text{ms}}^{-1}$
Negative sign shows that slow train appears to move westward w.r.t fast train with velocity of $5{\text{ms}}^{-1}$