Question on Newton's law of motion

[gaobo9109]

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

 

[py1sl]

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