Posted by **Chris** on Wednesday, November 7, 2012 at 7:33pm.

The radius of Earth is 3,959 miles. A spacecraft orbits 6 miles above the surface of Earth. The spacecraft completes 220° of a revolution around Earth in one day. What is the average speed of the spacecraft?

- Math -
**bobpursley**, Wednesday, November 7, 2012 at 7:52pm
This is a neat trick, as Earth is not spherical, the difference in radius at the poles compared to the Equator is 31miles.

Ignoring that bit of fact, assuming the Earth is spherical, and there is no atmospheric drag,then

period=1day=24hrs*3600sec/hr

speed=distancearund/tperiod=2PI(3959+6)/periodabove.

- Math -
**bobpursley**, Wednesday, November 7, 2012 at 7:53pm
oops, I missed the 220 degrees, so period=2PI(3965)*360/22O

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**Chris**, Wednesday, November 7, 2012 at 8:04pm
Hi Bob - I have 4 possible answers and cannot arrive at any of them by the above. My choices are (a)634mph (b)1038mph (c)761mph (d)113mph

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