Here is the question:
I have posted a link there to this topic so the OP can see my work.How fast is the distance between the friend changing when the distance between them is 210m?
A runner sprints around a circular track of radius 130 m at a constant speed of 4 m/s. The runner's friend is standing at a distance 210 m from the center of the track. How fast is the distance between the friends changing when the distance between them is 210 m? Round the result to the nearest thousandth if necessary.