You got to see the picture 1st. A block of mass m1 = 2 kg rests on a table with which it has a coefficient of friction µ = 0.66. A string attached to the block passes over a pulley to a block of mass m3 = 4 kg. The pulley is a uniform disk of mass m2 = 0.5 kg and radius 15 cm. As the mass m3 falls, the string does not slip on the pulley. -------- a) With what acceleration does the mass m3 fall? b) What is the tension in the horizontal string, T1? c) What is the tension in the vertical string, T3? ======================= Okay, shouldn't be that HARD of a problem. But this is what I've done so far. mass 1 (right is positive) ------- Summation of forces in x direction T1-u*m1*g=m1a Summation of forces in y direction N-m1g=0 N=m1g mass 3 (up is positive) ------ Summation of forces in y direction T3-m3*g=m3*a My biggest question is the following equation correct: mass 2 ------ (T1-T3)R=I*alpha simplifies to (T1-T3)R=.5*m2*R^2*(a/R) or (T1-T3)=.5*m2*a => is this right for mass 2 for net torque From here I manipulated the equations until I got a=... This is what I have so far, but I'm not getting the acceleration value right, unless I made an algebra error. But the equations look right so far, right?