Two passengers are on a moving sidewalk at the airport. Passenger A is standing still while passenger B is walking with a speed of 2.0 km/h. The sidewalk is moving west at a speed of 1.5 km/h. From the perspective of passenger B, what is the speed of passenger A?

Answer: V = - 2[m/s]

Explanation:

VA = velocity of passenger A, = 1.5 [km/h], it is the same velocity of the side walk

VB = 2+1.5=3.5 [km/h], that is the velocity observed by a person outside of the sidewalk

from the perspective of passenger B the speed of passenger A is VA-VB=-2[m/s]

it means that passenger B is seen how passenger A is getting closer and eventually passing him