1. The problem statement, all variables and given/known data A 0.2 kg disc slides down from smooth track of height 1.8m. It arrives at a rough 1 kg block resting on a smooth surface. The friction between them is 1.2N. Find the distance travelled by the disc on the block before it comes to rest relative to the block. 2. Relevant equations 3. The attempt at a solution use observer frame: velocity=6 m/s then I use conservation of linear momentum, because only internal forces. m1u1=m1v1+m2v2 0.2(6)=1.2(v) v=1 m/s f=1.2N to right on the block, to left on the disc a of disc=-6m/s^2 a of block= 1 m/s^2 for the disc, v^2-u^2=2as -35=2(-6)s s=35/12 m for the block, 1=2(1)(s) s=0.5 m so it moves 2.41 m on the surface but when I find the time required for the disc, v=u+at 1=6+(-6)t t=5/6 s for the block 1=0+(1)(t) t= 1s They are different? I know my answer of 2.41 m must be wrong, but where is my mistakes? thank you!