1. The problem statement, all variables and given/known data A block of mass m1 is on top of a block of mass m2. Block 2 is connected by an ideal rope passing through a pulley to a block of unknown mass m3 as shown. The pulley is massless and frictionless. There is friction between block 1 and 2 and between the horizontal surface and block 2. Assume that the coefficient of kinetic friction between block 2 and the surface, μ, is equal to the coefficient of static friction between blocks 1 and 2. Q1 : The mass of block 3 has been changed such that block 1 and block 2 are moving together with a given acceleration of magnitude a. What is the magnitude and the direction of the force of friction exerted by block 2 on block 1? Q2: What is the minimum value of m3 for which block 1 will start to move relative to block 2? 2. Relevant equations 3. The attempt at a solution Force of friction exerted by block 2 on block 1 to keep them both moving without one sleeping over another is [tex] m3g - μ(m1+m2)g = μm1g[/tex] Correct me where I'm wrong. minimum value of m3 for which block 1 will start to move relative to 2 is [tex]m3g>μm1g[/tex] Therefore, m3>μm1 Both my answers are wrong. Not able to go any where with this. Someone please explaing, and I'll solve.