The train is moving at 50 m/s and Emma is walking down the aisle with 1 m/s speed in the same direction of train. The relative velocity of Emma with respect to other passengers pf the train would be 1 m/s. This is because, the train is not moving relative to them and only emma is moving at 1 m/s. If a person observes from outside, Emma would have (50 +1) m/s = 51 m/s velocity.
relative velocity when two objects are moving in same direction as oberved from outside observer:
![v_(ab)=v_a+v_b](https://img.qammunity.org/2019/formulas/physics/high-school/v6rd04eu6m5m8m085vkw2z2h053n4p194j.png)
relative velocity when two objects are moving in the opposite directionas oberved from outside observer:
![v_(ab)=v_a-v_b](https://img.qammunity.org/2019/formulas/physics/high-school/2im96hshbj10uyj6ljeeywt14dimahbgsi.png)