Question 1
The total force needed to drag a box at constant speed across a surface with coefficient of kinetic friction μk is least when the force is applied at an angle θ such that
◦ sinθ = μk.
◦ cosθ = μk.
◦ tanθ = μk.
◦ cotθ = μk.
◦ secθ = μk.
Question 2
The vector sum of three co-planar forces
◦ must be zero.
◦ must be perpendicular to one of the three.
◦ must be parallel to one of the three.
◦ must be perpendicular to the plane.
◦ may have any direction in the plane.
Answer 1
tanθ = μk.
Answer 2
may have any direction in the plane.