Frames of Reference Practice Solutions

A girl is on a train that is headed East at 100 miles per hour. The girl is walking at 5 miles per hour

toward the back of the train.

1.

What is the speed and direction of the train if the girls is the frame of reference?

5 mph East.

Explanation:

If the girl is the frame of reference, we need to check the train's relative movement to the girl.

If the girl was not moving inside the train, the speed of the train would be zero, because the train and the girl would be moving together with the same speed and direction.

If the girl is moving 5 mph toward the back of the train, the movement of the train should be calculated considering the girl is fixed (not moving).

So the direction of the train movement would be the inverse of the girls movement (the girl is going West), then the speed and direction of the train is 5 mph and East.