A person `A` is sitting in one train while another person `B` is in the second train. The trains are moving with velocities `60 m//s and 40 m//s`, respectively, in the same direction. Then the velocity of `B` relative to `A` will be

Options

A. `100 m//s` in the direction of trains
B. `20 m//s` in the direction of trains
C. `100 m//s` in the direction opposite to that of trains
D. `20 m//s` in the direction opposite to that of the trains

Answer

D

Explanation

`vec v_A = 60 hat i, vec v_B = 40 hat i`
`vec v_(B//A) = vec v_B - vec v_A = 40 hat i- 60 hat i= -20 hat i`
So direction is opposite to that of trains.