Prove Impossible to Orbit Earth in <80 Minutes

[Plutonium88]

"Describe the objective, apparatus, and results of the cavendish expirment?"
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Question2: Prove (using algebra) that it is impossible to go around (orbit around) Earth in less than 80 min..

I honestly have never heard of this... can some one explain it to me? or give me some links about it?

 

[grzz]

re Cavendish expt just search on the web.
re 2nd part:
Do you know how to use F = ma for an object going in circular orbit about the Earth?