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 $ms ^{-1}$ ) of this person as observed from train B will be close to : (take the distance between the tracks as negligible)

• A. $30.5\, ms ^{-1}$
• B. $29.5\, ms ^{-1}$
• C. $31.5\, ms ^{-1}$
• D. $28.5\, ms ^{-1}$

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. $B$
$\vec{ V }_{ m / B }=\vec{ V }_{ m }-\vec{ V }_{ B }$
$=-1.8+36-(-72)=106.2 km / hr$
$=29.5 m / s$