I drew a diagram here to try and help:A lighthouse 1 km from a beach shore revolves at 10$\displaystyle \pi$ radians/minute. How fast is the light sweeping across the shore 2 km from the lighthouse?

I think it will have something to do with a triangle. So just to find the other side, I'll use the Pythagorean theorem and get $\displaystyle \sqrt{3}$. I already knew this because I recognized the 30-60-90 triangle, so I know the angles too, but I don't know if we need them yet.

What I don't understand is what the question is asking. I thought the light was going around at a constant speed of 10$\displaystyle \pi$ radians/minute? What speed do they want?