# Acceleration due to gravity - Help with equation. Thanks!

#### nukeman

1. Homework Statement

Here is the problem:

GIven the formula below, calculate the expected value of the accerlation, G (in m/s^2). THe mass and radius of Earth are 5.974x10^24 kg and 6.37 x 10^6 m, respectively.

Formula to use: g = G Me/r^2

How do I solve for g ? I keep messing up on calculation.

Thanks

2. Homework Equations

3. The Attempt at a Solution

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#### rock.freak667

Homework Helper
'g' is already the subject of the formula, so you just need to substitute the numbers into the equation.

#### nukeman

'g' is already the subject of the formula, so you just need to substitute the numbers into the equation.
Oh. So, it would then turn into:

g = G 5.974x10^24 / 6.37 x 10^6

?

So, would the answer be? 9.378x10^29

? That cant be rigbht

#### rock.freak667

Homework Helper
Oh. So, it would then turn into:

g = G 5.974x10^24 / 6.37 x 10^6

?

So, would the answer be? 9.378x10^29

? That cant be rigbht
Well 'G' is a constant such that G=6.67300 × 10-11 m3kg-1s-2

And you are dividing by 106,so you can't really get back 1029. Redo the calculation with the value of 'G' in it.

#### nukeman

Well 'G' is a constant such that G=6.67300 × 10-11 m3kg-1s-2

And you are dividing by 106,so you can't really get back 1029. Redo the calculation with the value of 'G' in it.
im real sorry, but you lost me with G

How do I do the calculation with Value G in it?

#### rock.freak667

Homework Helper
im real sorry, but you lost me with G

How do I do the calculation with Value G in it?
g=GM/r2

Just replace the letters with the numbers given.

#### nukeman

How do I calculate this? First, is this correct?

6.6726 x 10-11N-m^2/kg^2 x 5.974x10^24 / 6.37 x 10^6

#### rock.freak667

Homework Helper
How do I calculate this? First, is this correct?

6.6726 x 10-11N-m^2/kg^2 x 5.974x10^24 / 6.37 x 10^6
Your units are the same throughout, so you can leave out the units in the calculation. You also forgot to square the radius 'r'.

g= (6.67x10-11)(5.974x1024)/(6.37x106)2

#### nukeman

I tried it 2 diferent ways.

next: 9.8200

??

Homework Helper

#### nukeman

This is more or less correct.
Is there anyway you can check, or I can be sure?

:)

#### rock.freak667

Homework Helper
Is there anyway you can check, or I can be sure?

:)
Well we know that on Earth, g=9.81 m/s2, so your answer should be around that number. (Depending on how accurate your values are)

#### nukeman

Well we know that on Earth, g=9.81 m/s2, so your answer should be around that number. (Depending on how accurate your values are)
Great, good enough for me :)

Thanks VERY much for your help, really appreciate it!

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