1. The problem statement, all variables and given/known data Two packages at UPS start sliding down a 20 degree incline. Package A has a mass of 5kg and a coefficient of friction of 0.20. Package B has a mass of 10kg and a coefficient of 0.15. Package A is in front of Package B according to a diagram given. The distance between Package A and the bottom of the ramp is 2m. How long does it take for Package A to reach the bottom? 2. Relevant equations Kinematics Equations and Free-Body Diagrams yielded the following breakdown of all the forces, given in this form: (Force), (x hat) +/- (y hat) uk_(box) is the kinetic friction coefficient. Ff is the friction force Fg/Fn are obvious X_Y is the force X on Y 3. The attempt at a solution The very first thing I did was make a table of forces symbolically: For package A, assume a tilted axis of 20 degrees, with +x in the direction of the packages' motion. Fn, 0 + Fn Fg, mg sin 20 - mg cos 20 Ff, -uk_A(Fn) + 0 B_A, B_A + 0 Fnet, (M_a)(A_a) + 0 For package B, assume an identical axis. Fn, 0 + Fn Fg, mg sin 20 - mg cos 20 Ff, -uk_B(Fn) + 0 A_B, -A_B + 0 Fnet, (M_b)(A_b) + 0 The acceleation is constrained by A_a = A_b, allowing us to use one acceleration "a". I then get these final equations for: Package A X: mg sin 20 - uk_a(Fn) + B_A = M_a(a) Package A Y: Fn = mg cos 20 Package B X: mg sin 20 - uk_b(Fn) - A_B = M_b(a) Package B Y: Fn = mg cos 20 Now, I haven't the foggiest idea what to do. All I see are endless streams of unsolvable equations with two unknowns.