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.

Question

Quizplus · Accepted Answer

Both Velma and Mort are correct relative to their own reference frames. Velma measures the speed of the rock relative to the train, while Mort measures it relative to the Earth.

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