Velma, Inside a Train Moving at 20 M/s, Throws a Rock

Multiple Choice

Velma, inside a train moving at 20 m/s, throws a rock in the forward direction at 5 m/s. According to her the rock moves at 5 m/s. According to Mort, standing on Earth outside the train, the rock moves at [approximately] 25 m/s. Who is correct?

A) Mort, because he is standing on Earth.
B) The Wizard of Oz.
C) Neither, because there is no universal "best" reference frame.
D) Velma, because she threw the rock.
E) Both, relative to their own reference frames.