physics
posted by sandhu .
Lazydog and his tractor (1330 kg) are pulling a trailer (530 kg) up a 7° hill. The trailer wheels roll freely. What is the magnitude of the force in the coupling between the tractor and trailer when their velocity is 8.7 m/s up the hill and they are slowing down at a rate of 0.2 m/s2? (N)

The mass of the tractor is irrelevant.
The mass of the trailer, m = 530kg
The inclination, θ = 7°
The net downward force is due to gravity, equal to
F1=mg sin(θ)
The coupling pulls the trailer with a force (tension) of T such that the net force is downwards equal to
F1T=m(0.2)
Substituting F1, and solving for T
T=F1m(0.2)
=mg sin(θ) m(0.2) 
thanks a lot