Hi everyone here is the picture of the this plane/friction problem. http://phasedma.com/uploaded/Physics problem.JPG The question asks what are the minimum and maximum values of m1 in the figure to keep the system from accelerating... Take µk = µs = 0.50 ------------------------ Ok when drawing my free body diagrams I have come up with this method of solving the problem... tell me if you agree. The force of friction can either be up or down the slope, if m2 = 0 or sufficiently small, then m1 would tend to slide down the plane. so Ffr would be directed Up the incline. We know that newtons second law for the y direction (i chose my xy coordinate axes along the plane-- IE horizontal x being the plane) shows that Fnormal - m1*g*cos(30) = m1*ay = 0 since theres no y motion Fnormal = m1*g*cos(30) Now for the x motion... For the first case (smallest m1) f = ma shows that m1*g*sin(30) - Ftension - Ffr = m1*ax <---- x direction since we want ax to be 0, we can solve Ftension since thats related to m2. Since Ffr can be AT MOST µs * Fnormal= µs*m1*g*cos 30 the minumum value m2 can have to prevent motion (ax = 0) is (after dividing by g) m2 = m1 * sin(30) - µs*m1*cos(theta). And then finding the max value wouldnt be much more difficult from there since we already set up our equations.. Am I correct here? If you are willing can someone work it --- what range do you get for the mass? Thanks for you help. Mechanics gets soooo tough!