Here is the problem I am working on: http://img45.imageshack.us/img45/5566/image0002bv6.jpg [Broken] Here is my work: http://img177.imageshack.us/img177/7127/image0001zy6.jpg [Broken] I cannot solve (2) for v since there are no real roots. When I set up the net forces in the x-direction in (1), should I have made [tex]ma_c[/tex] negative? I think it makes sense if [tex]ma_c[/tex] is negative because it tells us that the acceleration vector is always pointing in the negative x-direction. In all of the other Newton's second law problems, I never had to make the side with [tex]ma[/tex] negative. Why in this problem must I now specify the sign of the acceleration?