1. The problem statement, all variables and given/known data The drawing shows a large cube (mass = 25 kg) being accelerated across a horizontal frictionless surface by a horizontal force P. A small cube (msmall = 4 kg) is in contact with the front surface of the large cube and will slide downward unless P is sufficiently large. The coefficient of friction between the cubes is f = 0.71 . What is the smallest magnitude that P can have in order to keep the small cube from sliding down? 2. Relevant equations Ffriction= f*mg 3. The attempt at a solution Ffriction=msmall*g f*P=msmall*g P=56,34N But the answer must be P = 400 N.