9709 Pure 1 · 1.3 Coordinate Geometry · where the math is actually used
An emergency planner in St. Croix is watching a storm. Over a few hours a storm's path is close to a straight line, so we model it as one. These storms are made up, not real storm data. How close does it come, does it enter the warning circle, and when?
1 grid unit = 10 km. Drag S₁ and S₂, or tab to one and use the arrow keys.
Work it out
Steps 5 and 6 answer these. Make a guess from the picture before you reveal them.
Why the perpendicular. The shortest distance from a point to a line is along the perpendicular. That is why the method finds the gradient −1/m and the line through C with that gradient: where it meets the track is the closest point F.
How far to trust it. A real track curves and the speed changes, so this straight-line model is for the next few hours only. Planners redo the calculation every time a new position comes in.