A small box is held in place against a rough vertical wall by someone pushing on it with a force directed upward at 25o above the horizontal. The coefficients of static friction and kinetic friction between the box and wall are 0.21 and 0.51, respectively. The box slides down unless the applied force has magnitude 43-N. What is the mass (in kg) of the box?

Question

A small box is held in place against a rough vertical wall by someone pushing on it with a force directed upward at 25o above the horizontal. The coefficients of static friction and kinetic friction between the box and wall are 0.21 and 0.51, respectively. The box slides down unless the applied force has magnitude 43-N. What is the mass (in kg) of the  box?

bobpursley · Answer

normal force=F*cos25 friction force= .51*F*cos25 downward force= mg-F*sin25 setting downward force= friction force mg-41*sin25=.51*41*cos25 now solve for mass m.