I saw this question ona game show, but never found out the answer... now I need the answer to settle a bet! 'If you are on a train traveling north at 5 mph, and you are walking toward the back of the train at 2 mph, how fast are you moving? '

I believe that you would be moving at 5 mph because you will still be going the same speed as the train as you walk towards the back at 2 mph. Im not quite sure though I would ask a math teacher... although I'm pretty sure I'm right.

5 mph.

Come on people! The people you pass as you walk back through the train are moving at 5 mph. They will get to each point before you do. Therefore you are going slower than them. So, 3 mph.

Definitely 3mph.

I third 3mph.

Its not even "real physics" folks. No complicated vector calculations needed.

Imagine you were walking at 5mph towards the back as the train was moving forwards at 5mph. If you looked out the window, the station would be stationary.

The same logic applies here.

Velocity is always relative. You will be moving +3mph relative to the earth but -2mph relative to the train. You will be moving at various other speeds in various other frames of reference.

Yes, in the reference frame of the center of the universe, you're moving several thousand kilometers per second ;)

It is true the question didn't say how fast in relation to what. I don't see any reference that would give 5 mph as the correct answer. The point of walking 5 mph leaving you stationary to the station was a good one.

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Originally Posted by Brihead

I saw this question ona game show, but never found out the answer...now I need the answer to settle a bet!! 'If you are on a train traveling north at 5 mph, and you are walking toward the back of the train at 2 mph, how fast are you moving??'

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Still going north but at only 3 miles per hour

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Originally Posted by labman

I don't see any reference that would give 5 mph as the correct answer.

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Well, the reference point of a person walking toward the end of the train on the station at 2mph

Speed (unless you're moving at the speed of light) is always relative. If you don't specify a frame of reference, one is assumed. Normally, the assumed frame of reference is the earth. That being the case, the answer is "north at 3 mph". If you want to change your frame of reference to a person sitting on the same train, the answer is "towards the back at 2 mph".

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Originally Posted by Capuchin

Well, the reference point of a person walking toward the end of the train on the station at 2mph

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Good one! ;)

So Brihead, did you win the bet? Or your opponent?