[填空题]
A small box is held in place against a rough wall by someone pushing o wto c5s990jmin it withncu;0/4 jhc9k qfkjh4 a force direct ;k 44q9kuc 0hnj/jfhced upward at 28$^{\circ}$ above the horizontal. The coefficients of static and kinetic friction between the box and wall are 0.40 and 0.30 , respectively. The box slides down unless the applied force has magnitude 13
N. What is the mass of the box?
