those are my problems: ok for the first one: Xcm=(1/M)[(5)(m/6)+(15)(m/6)+(5)(m/6)+(5)(m/6)+(15)(m/6)+(25)(m/6)] Xcm=(35/3)=11.667 Ycm=(1/M)[(25)(m/6)+(25)(m/6)+(15)(m/6)+(5)(m/6)+(5)(m/6)+(5)(m/6)] Ycm=(40/3)=13.333 so the CM of mass is (11.667,13.33), which is not even on the surface, so i think its wrong. Any suggestions? Second one: 45kg woman is in a 60kg canoe of length 5m. They are initially at rest. she walks from a point 1m from the end to a point 1m from the other end where she stops. If resistance and the motion of the canoe in the water are ignored, how far does the canoe move during the process. Im totally lost on this problem, i dont know how to start. I have a feeling the C of M doesnt change, but im not sure. Know a way to start me off? Conservation of Momentum? Since she moves 3m, was thinking something like this: (3m)(45kg)=(Xm)(60kg) X=2.25 but not sure. Thank you for your time and patience!