Question

for the friction on an inclined plane , why is it important that the pulley is positioned such that the rope is parallel to the surface of the plane. ( you may want to sketch a picture below to help explain your answer)

Answer 1

You want to know the force on the plane due only to the weight of the object times the cosine of the angle of the plane N = W cos(@). If the rope is parallel to he plane, it will not add to or reduce this normal force, N. The coefficient of friction will then be mu = F /N, where F is the measured force parallel to the plane minus W sin (@).