# physics

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A heavily loaded freight train moves with constant velocity. What is the relationship between the net force on the first car (F1) and the net force on the last car (F2)?
A. F1=F2
B. F1>F2
C. F1<F2
D.unable to determine

Would it be choice a?

• physics -

the velocity is constant so there is no net force on the entire train.
There is however a force back on the engine from the drag of all the cars. It is equal to the thrust from the engine wheels
It is biggest between the engine and the first car, being the sum of drags from all the cars behind
HOWEVER!!!
since each car moves at constant velocity, the NET force on each car is zero.
As the net drag decreases moving back on the train, the net thrust also decreases by the same amount.
so
A
F1 = F2

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