If you run 10mph inside of a train that is moving 100mph, are you moving 110mph or 100mph?

Question

If you run 10mph inside of a train that is moving 100mph, are you moving 110mph or 100mph?

In: Physics

Answer 1

Relative to a stationary observer on the ground:

0 – (100 + 10) = -110

You’re travelling 110 mph away from the observer.

Relative to train, running from back to front:

100 – (100 +10) = 10

You’re travelling 10 mph towards the front.

Relative to train, running from front to back:

100 – 10 = 90
You’re travelling 10mph away from the front.