Determining angle to which satellite is visible

[unscientific]

Homework Statement

An Earth satellite is moving in the plane of the Earth's equator. Satellite is 1680km above Earth's surface, with a period of 2 hours. Determine the angle through which satellite is visible to an observer at an equator, measured about the centre of the Earth.

Homework Equations

the first part involved finding the height above the satellite, which I have found to be 1680km. This is the second part. I know a geometrical approach is required, but can't seem to draw it out.

The Attempt at a Solution

Tried drawing a sphere and satellite but can't seem to work it out.. Appreciate help! (Already tried but failed to understand the provided answers)Original souce: question 2b(iii) of http://www.physics.ox.ac.uk/olympiad/Downloads/PastPapers/BPhO_Paper2_2006_QP.pdf

Answer: http://www.physics.ox.ac.uk/olympiad/Downloads/PastPapers/BPhO_Paper2_2006_MS.pdf

 

[Spinnor]

I think drawing an accurate picture helps. Does this drawing help? You have two lengths of a triangle, problem started?

 

[unscientific]

so I assume the guy is at the top, and since the line is a tangent to his line of sight, any where lower than the tangent, the line produced will cut through the Earth's surface, resulting in the satellite being blocked.

Is that analogy correct?

 

[Spinnor]

Give or take a little I think the sketch is the geometry you are looking for.