Mass and Radius of Earth

[MDwannabe7]

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At what height above the earth's surface is the acceleration due to gravity 10% of that at sea level?

Obviously, F=Gm1m2/r^2; G=6.6 x 10^-11; a @ sea level = 9.8 m/s^2

I cannot figure out how to solve this problem without knowing either the mass or the radius of the earth. Thus and therefore, unless one of you brilliant people out there can explain this to me, my next question is: are we therefore expected to know the mass and/or radius of the earth for the MCAT?

help

 

[mosquitoman]

they always tell you mass and radius if they are necessary in the problem

F = G * m1m2/r^2
F =ma = mg

mg = G * Mem2/r^2

masses cancel out

g = G * Me/r^2
so if we want to make g 1/10 of what g is...

r^2 = G * Me /.1g


you need mass of earth to get a numerical value...

unless they want you to say it is 3.3 * the radius of the earth (sqrt10)