Question on Newton's law of motion

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SUMMARY

The discussion centers on a physics problem involving Newton's laws of motion applied to a train with three coaches: A, B, and C. Coaches A and C each have a mass of 10,000 kg and driving forces of 20,000 N and 18,000 N, respectively, while coach B has a mass of 8,000 kg and experiences a drag force of 6,000 N. The user initially calculated the net force on coach A incorrectly, leading to a misunderstanding of the overall system dynamics. The correct approach involves analyzing the entire train system to account for all forces acting on each coach.

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gaobo9109
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Homework Statement


A train consists of three coaches A,B and C linked together via tow bars. A and C are coaches with engines and have a mass of 10000kg each, while B is an un-powered coach having a mass of 8000kg. The driving force of the engines in A and C are 20000N and 18000N respectively. The drag force on A is 9000N while B and C experiences the same drag force of 6000N.


Homework Equations


Newton's three laws


The Attempt at a Solution


I tried to find the net force exerted on coach A by
F(net) = 20000 - 9000 = 11000N
a = 11000/10000 = 1.1m/s2
However, the answer given is 0.61m/s2
Can anyone tell me where did I go wrong? Thanks
 
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Hi Gaobo,

The question gives you extra information which you haven't used which is key to getting answer.
I suggest you draw a picture and consider the entire train, currently you have missed the forces relating to coaches B and C.

Hope this helps
 

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