Sliding Block Problem (Please Help!) http://img441.imageshack.us/img441/1809/physicsyj6.jpg [Broken] The drawing shows a large cube(mass=25 kg) being accelerated accross a frictionless surface by a horizontal force P. A small cube(mass=4.0 kg) 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 in 0.71. WHat is the smallest magnitude that P can have in order to keep the small cube from sliding downward? What i did: 4.0 x 9.8 = 39.2 x 0.71 = 27.832 N 39.2 - 27.832 = 4.0a a = 2.842 m/s/s I do not know what the acceleration in the x direction must be in order to make the acceleration upward match 2.842.