A beaver is pulling a small branch of mass m up a hill at a constant velocity. The hill slope is at an angle θ above the horizontal. The coefficient of friction is μk. State how much force he must exert on the branch as he pulls it parallel to the slope in terms of the variables stated in this problem.
(a) mg sin θ + μkcos θ
(b) mg sin θ + mgμk cos θ
(c) mg cos θ + mgμk sin θ
(d) None of the above