[روح الورد 2010]

يا استاذ لو سمحت ماعرفت هذا السؤال
Tow forces act upon a 5.0 kg box.One of the forces is F1=(6.0i+8.0j)N.If the box moves at a constant velocity of (1.6i+1.2j) m\s,what is the second force?