Calculate thow long it would take a ball to orbit the earth once , just above the surface , at a speed of 7920 ms^-1 . The radius of earth is 6400km.
Well Im not sure to be honest.
The Attempt at a Solution
I tried using S=ut+1/2(a)(t)^2
Then used (-b +/- √b^2-4ac)/2a
But got stuck in (-b +/- √b^2-4ac)/2a because got a negative sign answer in the √
Cant find a formula in the book for this - probably have to manipulate some other formulas, but as I said im not sure