1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

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
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook