Question

What force would you have to exert on a 324 N trunk up a 19 degree inclined plane so that it would slide down the plane with a constant velocity? What would be the direction of the force? The coefficient of friction between the plane and the trunk is .322.

Answer 1

Break the weight of the trunk into two components, one down the plane, and one normal to it.

Forcedownplane=mg*sinTheta
Forcenormal=mg*cosTheta

Then, the force of friction is down, as motion is upward mu*mg*cosTheta

Summing forces up the plane:

F-mu*mg*cosTheta - mg*sinTheta=ma=0
solve for F. ma is zero because of zero acceleration (constant velocity)