1. The problem statement, all variables and given/known data **12. A physicist plants a vertical pole at the waterline on the shore of a calm lake. When she stands next to the pole, its top is at eye level, 175 cm above the waterline. She then rows across the lake and walks along the waterline on the opposite shore until she is so far away from the pole that her entire view of it is blocked by the curvature of the surface of the lake, that is, the entire pole is below the horizon (Figure 1.18). She finds that this happens when her distance from the pole is 9.4 km. From this information, deduce the radius of the Earth. 2/3. Relevant equations, solution attempt My attempt at a diagram. One of the green parts is approximated: http://img.skitch.com/20091025-k8cm5ie32ifdecsm3fa49y3d3e.jpg I tried a number of approaches. At first I didn't know whether to think of the 9400 meters in terms of length of a curve, or in terms of a straight line, but then I decided it was negligible considering the solution. I tried working backwards from the arc length. I tried SOHCAHTOA and the Pythagorean Theorem. Not sure quite what to do here. What is wrong about how I am thinking? Thank you.