A heavy crate of mass m m\,m is pulled up a rough ramp inclined at an angle θ \theta\,θ to the horizontal by a rope. The rope is parallel to the ramp and exerts a constant tension TTT. The crate is observed to move up the ramp at a constant velocity.
Which of the following expressions correctly gives the magnitude of the frictional force F F\,F acting on the crate?
F=T+mgsinθF = T + mg \sin\thetaF=T+mgsinθ
F=T−mgsinθF = T - mg \sin\thetaF=T−mgsinθ
F=mgsinθ−TF = mg \sin\theta - TF=mgsinθ−T
F=T−mgcosθF = T - mg \cos\thetaF=T−mgcosθ