Question

Train $A$ and train $B$ are running on parallel tracks in the opposite directions with speeds of $36$ km/ hour and $72$ km/hour, respectively. A person is walking in train $A$ in the direction opposite to its motion with a speed of $1.8$ km/ hr. Speed (in $m{s}^{-1}$ ) of this person as observed from train B will be close to : (take the distance between the tracks as negligible)

• A. $30.5m{s}^{-1}$
• B. $29.5m{s}^{-1}$
• C. $31.5m{s}^{-1}$
• D. $28.5m{s}^{-1}$

Answer 1

Answer: (B)

Velocity of man with respect to ground
${\vec{V}}_{m/g}={\vec{V}}_{m/A}+{\vec{V}}_A=-1.8+36$
Velocity of man w.r.t. $B$
${\vec{V}}_{m/B}={\vec{V}}_m-{\vec{V}}_B$
$=-1.8+36-(-72)=106.2km/hr$
$=29.5m/s$