Mass of a planet using a pendulum

[Frostfire]

Homework Statement

An explorer wants to find the mass and radius of a planet he has landed on. He uses a pendulum he has with him and observes it takes a period of T1 to complete. He then climbs 2km up and observes period t2. Find planetary Radius r and Mass m

Homework Equations

g = GM/r^2

T = 2pi(sqrt(L/g)

The Attempt at a Solution

g= 4pi^2L/T1^2 = Gm/r^2 #1

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4pi^2L/T2^2= Gm/(r^2 + 2000)#2

I took #1 and solved for r,

r=sqrt((GMT1^2)/4pi^2L)


input that in two and came up with

GmT1^2 + L8000pi^2= GmT2^2

after canceling

M=8000pi^2L/G(t2^2-T1^2)

when i evaluate this I get a reasonable mass, 5.~ *10^15 but my radius is way to small



any thoughts?

 

[mgb_phys]

(r^2 + 2000) is not the same as (r+2000)^2

 

[Frostfire]

(r^2 + 2000) is not the same as (r+2000)^2

ya sorry type o there,