Tension acceleration train problem

AI Thread Summary
To determine the pull on the last car of the train, the user calculated the acceleration using the total mass and engine pull, resulting in an acceleration value. They then applied Newton's second law to find the tension (T1) while accounting for the friction force of 680N acting against the last car. The user expressed confusion over not arriving at the correct answer and sought clarification on their approach. A key point raised in the discussion is the need to consider whether friction adds to or subtracts from the tension experienced by the last car. Understanding the role of friction in this context is crucial for solving the problem accurately.
cheez
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Find the pull in Newtons on the last car of this train. There are two cars. The last car has a mass of 850kg and friction (brakes) of 680N. The other car has a mass of 1700kg. the engine has a mass of 6000kg and a pull of 1000N
Let T1 be the pull on the last car of the train
I tried to solve this problem by calculate the acceleration first. I used this equation F=ma a=F/M = (1000N)/(6000kg+850kg+1700kg)
And then I used T1-f = ma T
1-680n = 850kg x a from the above answer

But I didn't get the answer. Can anyone point out my mistake? thanks so much!
 
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Think about the physics of the problem. Would friction add to or subtract from the pull on the last car?
 

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