Kinematics

JEE Main level, single correct, medium

146 of 308

Question 146 of 308

Train AA and train BB are running on parallel tracks in the opposite directions with speed of 36kmhour−136km{hour}^{-1} and 72kmhour−172km{hour}^{-1}, respectively. A person is walking in train AA in the direction opposite to its motion with a speed of 1.8kmhour−11.8km{hour}^{-1}. Speed (inms−1)\left(inm{s}^{-1}\right) of this person as observed from train BB will be close to: (take the distance between the tracks as negligible)

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Answer: (A) 29.5ms−129.5m{s}^{-1}

VMA=−1.8kmhr−1=−0.5ms−1\begin{matrix}{V}_{MA}=-1.8km{hr}^{-1}=-0.5m{s}^{-1}\end{matrix}
Vman,B=Vman,A+VA,B\begin{matrix}{V}_{man},B={V}_{man},A+{V}_{A},B\end{matrix}
=Vman,A+VA−VB\begin{matrix}={V}_{man,A}+{V}_{A}-{V}_{B}\end{matrix}
=−0.5+10−(−20)\begin{matrix}=-0.5+10-(-20)\end{matrix}
=−0.5+30=-0.5+30
=29.5ms−1=29.5m{s}^{-1}

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