Hi, I''m trying to find an equation to find at what moment T a moving point will colide with a rotating plan P. I''m thinking of using the dot product between the Normal Vector of that plan and the distance between the moving point and a fixed point located on the plan. This give me the following equation: Mp = Moving Point = Xx + Yy + Zz + VxT + VyT + VzT Fp = Fixed Point. = Yy (not moving, located on the rotating axis) Rv or n = Rotating Normal = Cos(WT + Phi)x + Sin (WT + Phi)z + Yy W = Angular velocity Phi = Angular position at moment 0. F = ((Yfp - Ymp)+ VyT)*Yn + ((-Zmp + VzT)*Sin(WT + PHI)) + ((Xfp - Xmp) + VxT)*Cos (WT + PHI)) Can anyone help me resolve that equation ??? Thanks. Nick

Take a differant approach. Your velocity can be split into a components orthogonal and parallel to the normal. So basically you are going to hit the plane when the magnitude of the component parallel times the time equals the current distance from the plane. So to find the time divide the distance from the plane by the magnitude of the component parallel.