Question 143 of 308

Train A is moving along two parallel rail tracks towards north with $72km{h}^{-1}$ and train $B$ is moving towards south with speed $108km{h}^{-1}$. Velocity of train $B$ with respect to $A$ and velocity of ground with respect to $B$ are (in $m{s}^{-1}$):

A$-30$ and $50$B$-50$ and $-30$C$-50$ and $30$D$50$ and $-30$

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Answer: (C) $-50$ and $30$

${V}_{A}=72km{h}^{-1}=72\times \dfrac{1000}{3600}=20m{s}^{-1}$ and
${V}_{B}=-108km{h}^{-1}=-108\times \dfrac{1000}{3600}=-30m{s}^{-1}$
Velocity of $B$ w.r.t. $A$:
${V}_{B/A}=-30-20=–50m{s}^{-1}$
Velocity of ground w.r.t. $B$:
${V}_{G/B}=0-\left(-30\right)=30m{s}^{-1}$