Physics question?

Question

you push a 325-N trunk up a 20 degree inclined plane at a constant velocity by exerting a 211-N force parallel to the planes surface. What is the sum of all forces parallel to the planes surface?
Can someone explain how to solve this?

Answer 1

F=Ff-Fd-f

F - Resulting force
Ff - forward force up the incline
Fd - Force downward due to trunks weight W
f- force of friction

Ff= 211 N
Fd= W sin(20)=325 sin(20)=111 N
f= u W cos(20)= 0 if coefficient friction u=0

For constant velocity F=0 we

F=Ff-Fd-f =0
Ff-Fd -f=0
f is not zero
f= Ff - Fd=211 - 111= 100N