An airplane is traveling at a speed of 200 m/s relative to the Earth. A person walks toward the front of the plane at a speed of 1 m/s. How fast is that person traveling in reference to the other people on the plane?

1 m/s

Explanation:

This is because, everybody in the plane including the person walking is moving at the speed of the plane which is 200 m/s. Now, when the person starts to walk with a speed of 1 m/s, his relative velocity to the other passengers is 1 m/s since he is already moving at the speed of the plane before starting to walk.

His velocity relative to the ground V' = velocity of plane relative to ground, V + velocity of person relative to plane, v

V = 200 m/s and v = 1 m/s

So, V' = 200 m/s + 1 m/s = 201 m/s

Since the velocity of the other passengers is the velocity of the plane, V = 200 m/s. The velocity of the person traveling in reference to the other people on the plane is V" = V' - V = 201 m/s - 200 m/s = 1 m/s

365.25 earth days are in the year of a light year