(I know this type of problem has been discussed on here before, but I still don't understand what to do next) The attached drawing shows a large cube (mass=55kg) being accelerated across a horizontal frictionless surface by a horizontal force P. A small cube (mass=4.5kg) is in contact with the front surface of the large cube and will slide down unless P is sufficiently large. The coefficient of static friction between the cubes is 0.55. What is the smallest magnitude that P can have in order to keep the small cube from sliding downward? So far I have found that: Normal force=ma, (4.5 x 9.81)= 44.1 N F sub s=Mu sub s times mg, (.55 x 44.1)=22.05N I've also attatched a diagram of all the forces acting on the small cube, and concluded that an additional force of 22.05N is necessary to keep the small cube on the large one. I just don't know where to go from here to find P. Thanks for your help.