A train is moving slowly on a straight track with a constant speed of 2 ms^-1. A passenger in that train start walking at a steady speed of 2 ms^-1 to the back of the train in the opposite direction of the motion of the train. So to an observer standing on the platform directly in front of that passenger appears to be

CONCEPT:

The velocity of A with respect to B is ​​VAB and

​V_AB = V_A - V_B

The velocity of A with respect to ground VAg

V_Ag = V_A - V_g = V_A - 0 = V_A

VAg = VA

CALCULATION:

V_t = 2 m/s

V_pt = -2 m/s

V_t - V_g = 2

V_p - V_t = -2

V_p - V_g = 0

Vp = 0

So the velocity of train = 0

Hence the passenger standing on the ground will observe the passenger in rest.