Question

Train A is moving along two parallel rail tracks towards north with speed 72 km/h and train B is moving towards south with speed 108 km/h. Velocity of train B with respect to A and velocity of ground with respect to B are (in ms^–1) : 

(1) –30 and 50 

(2) –50 and –30 

(3) –50 and 30 

(4) 50 and –30

Answer 1

(3) –50 and 30 

\(V_{B/A}=\vec {V}_B-\vec{V}_A\)

= – 30 – 20 = –50

\(\vec{V}_{g/B}=\vec {V}_g-\vec {V}_B\)

= 0 - (-30) = +30 

-50 and 30