This appeared at first to be simple but it is abit out of the ordinary here is my attempt at solving it,
I am assuming that the velocity of the car and trailer isnt constant as forces are unbalanced...(more friction than driving force)
Therefore Force going in uphill direction = 700 N
Force (or friction) going downhill =
*12000)
=7000N
However These are irrelevant as we are interested in the difference of the net forces acting on the trailer and car
Let up hill be negative and downhill be positive
Net force acting on the car is equal to
-700=3400)
Net force acting on the trailer is equal to
=2900)
Car has more force than trailer downhill therefore 0 tension in the tow bar as the car and trailer will both be going backwards, i feel as if you are leaving some information out...is the car going downhill or up hill etc...