1. The problem statement, all variables and given/known data This is a 2-part question 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, mu, is equal to the coefficient of static friction between blocks 1 and 2. (Question 1)The mass of block 3 is 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? Express your answer in terms of some or all of the variables a, m1, m2, mu , and g (acceleration due to gravity). To indicate the direction, use a minus sign if the force is pointing to the left. (Question 2)What is the minimum value of m3 for which block 1 will start to move relative to block 2? Express your answer in terms of some or all of the variables m1, m2, \mu, and g. 2. Relevant equations F=ma 3. The attempt at a solution For part 1 I tried to find the force of friction by finding the force that opposes it (the force of motion) and putting a negative sign on it because friction opposes motion. I ended up getting F=mu*(m1+m2)*g For part 2 I rearranged Newton's 2nd law to get m=F/a. I then found the force of the system to be mu*(m1+m2)*g and the acceleration to be g. Using the modified Newton's second, I got (m1+m2)*mu. I know the answer to both of these is wrong because I am taking an online course (so I know whether I am right or wrong instantly). If someone could take his/her time to help me get the right answer (and more importantly how to find the right answer), I would be grateful. Thanks in advance.