Question

Two parallel rail tracks run north-south. On one track train A moves north with a speed of 54 km $h^{-1}$ and on the other track train B moves south with a speed of 90 km $h^{-1}$. The velocity of train A with respect to train B is :

• A. 10 m $s^{-1}$
• B. 15 m $s^{-1}$
• C. 25 m $s^{-1}$
• D. 40 m $s^{-1}$

Answer 1

The correct option is D 40 m $s^{-1}$

Speed of train A : $v_a=54km/h=54\times 5/18m/s=15m/s$
Speed of train B= $v_b=-90km/h=-90\times 5/18m/s=-25m/s$

Relative velocity of ground with respect to B is $v_{ab}=v_g-v_b$
$=15-(-25m/s)$
$=+40m/s$