Question on Newton's law of motion

AI Thread Summary
The discussion revolves around a physics homework problem involving a train with three coaches and their respective forces. The user calculated the net force on coach A but arrived at an incorrect acceleration of 1.1 m/s² instead of the correct 0.61 m/s². A key point raised is that the user overlooked the forces acting on the entire train, particularly the interactions between coaches B and C. It is suggested to visualize the problem and account for all forces to arrive at the correct solution. Understanding the complete system dynamics is essential for applying Newton's laws accurately.
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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