Here it is. A 10 kg suitcase is placed on a flat ramp inclined at 37 deg. When released from rest, the suitcase accelerates down the ramp at .15 m/s^2. What is the coefficient of the kinetic friction between the suitcase and the ramp? Now, from this I got Fnet=m*a=1.5 N in the x direction. Fnet=Fx-kinetic friction=mg(sin theta)-mg(cos theta)(mu k) solving for mu k: mu k=mg(sin theta)-Fnet)/mg(cos theta) Doing all the math gets me something like .46, but the back of the book disagrees. What am I doing wrong?