1. The problem statement, all variables and given/known data https://dl.dropbox.com/u/51681259/physics_diag.png [Broken] Object C & P are moving at the same constant velocity to the right, in the configuration of the image. The friction between object C and the ground is 0. Suddenly the friction increases to μ=0.9 between the ground and object C. This makes object C decelerate to a stop over 4m. At what velocity does object P impact the right internal side of object C. There is no friction between C & P. d = 1m (distance between p right side and c internal right side) μ = 0.9 s = 4m (stopping distance) 2. Relevant equations I can fine object c's initial velocity by combining a couple of formulas: F_net=ma F_friction=μmg v^2=u^2+2as I find the initial velocity of C & P as being 8.4m/s. Then I can find the acceleration of C, relative to the ground, after the increase in fiction which turns out to be: -8.82m/s/s And that means that relative to C, P accelerates forward at 8.82m/s/s. <IS THAT CORRECT??> Then I take p's relative acceleration and the initial velocity and put them through v^2=u^2+2as and find: v^2=8.4^2+(2*8.82*4) v=9.39 So my answer is that P impacts C at 9.39 m/s. Is this even close to correct?