A floating passenger car

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-----Original Message-----
From: DW [*addy removed by aliens*]
Sent: Tuesday, November 19, 2002 9:32 PM
To: questions@stupidquestionsanswered.com
Subject: I have a stupid question!

...hhhmmm... O.K. Here it is... You have a really long train going up a hill. One locomotive engine in the lead spot, and one locomotive engine in the last position. Odd number of passenger cars in between them, all exactly the same weight. The two engines are pushing/ pulling the exact same amount. Which engine is moving the middle passenger car?? Are both couplings "floating" on that car??

In the question, both engines are supplying the same amount of power to pull/push the train cars and the writer asks about which engine is moving the middle car. Is the power of the engines somehow canceling each other out so that the center car is "floating" between them?

Nope. The "center" of the train is not the middle car itself, it is a point in the center of the middle car. The front half of the car is being moved by the lead engine, while the back half of the car is being moved by the rear engine.

Uncle Joe. Thanks Uncle Joe. Technical answer:

If they are truly push/pulling the same amount, and the two engines weights are the same, and each of the cars all weight the same, then each engine is moving half the load which would mean half of the middle car. For example if there are three passenger cars then the first car's lead coupling is in tension with the load of 1.5 cars. Its trailing coupling is in a .5 tension with car 2. The second cars trailing coupling is in compression with half a cars load, and the 3rd cars trailing hitch is in compression with 1.5 car loads. Each engine carries its own load. That's it! -Darnley