# Pendulum gravity on X planet ratio

1. Jul 26, 2009

### missnola2a

1. The problem statement, all variables and given/known data

Now you take off to an unknown planet with the same pendulum as in part (a). You measure the period of the pendulum on that planet and you find it to be twice as much compared to the one of the pendulum while on Earth. What is the ratio of ge on Earth to the gx of the unknown planet?

2. Relevant equations

I tried inputting arbitrary numbers and I came up with a ratio 2.585/1, but its not right,

T=2pi * sqrt (L/G)

3. The attempt at a solution

2. Jul 26, 2009

### Feldoh

Can you show your attempted work? I'm getting around 2.45...

I should note that the gravity of planet x is 2.45, that is NOT the ratio the ratio of 9.8/2.45 is ~ 4.

Last edited: Jul 26, 2009
3. Jul 26, 2009

### missnola2a

I used L 10 on earth and planet X and got T = 6.34 on earth, then doubled it and solved for X grav and got 2.4525

resulting in 2.587:1 which isnt right.

i did the same thing with L 50 on earth and got a different ratio.... ehhhkkk!

4. Jul 26, 2009

### ralilu

the ratio is 4. if T = 2pi x sqrt(L/G) then 2T = 2pi x sqrt(L/(1g/4))

5. Jul 26, 2009

### missnola2a

4e/1x??

or
1e/4x

6. Jul 26, 2009

### rock.freak667

so if you know that

$$T= 2\pi \sqrt{\frac{l}{g_e}}$$

and

$$2T=2\pi \sqrt{\frac{l}{g_x}}$$

can you divide those two and thus get the ratio gE/gX?

7. Jul 26, 2009

### ralilu

4e:1x
It might look like a scary question but its a simple math problem and like rockfreak said you could've just divided the two (ratio just means divide) :)