Circular Motion of a ball around the earth

[Psycotic.Goth]

Homework Statement

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.

Homework Equations

Well I am 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 I am not sure

 

[JaredJames]

If you know the radius of the earth, you can calculate the circumference.

You know the speed of the ball.

With those two pieces of data you can calculate the time taken to complete the journey:

Time = Distance / Speed

No need for SUVAT equations here.

Jared

 

[Psycotic.Goth]

Thanks a lot Jared - I feel dumb now for using SUVAT lol

-PsyG