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Homework Help: Question on Newton's law of motion

  1. Apr 9, 2010 #1
    1. The problem statement, all variables and given/known data
    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.

    2. Relevant equations
    Newton's three laws

    3. 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
  2. jcsd
  3. Apr 9, 2010 #2
    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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