physics
posted by ash .
A couch with a mass of 100 kg is placed on an adjustable ramp attached to a truck. As one end raises, the couch begins to move downward. If it sldes with an acceleration of .79 m/s^2 at 12 degrees, what is the coefficient of kinetic friction.
I still am having troubles with this problem.

So, it is sliding down this 12 degree ramp. It does not matter that a truck is attached. The truck is not moving.
The weight of the couch provides a force down the ramp of
M g sin 12 = 203.8 N
The net force acting on the couch in that direction is
Fnet = M*a = 79 N
But
Fnet = 203.8  Ffriction
Therefore
Ffriction = 124.8 N
The kinetic friction coefficient (Uk) can be obtained from
Ffriction = M*g*cos12 *Uk = 124.8 N 
Thanks!I get it now. I had gotten the normal force, but I wasn't sure how to get the force of friction, but this helps.