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

## 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

## 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.

'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.

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.

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

I tried it 2 diferent ways.

next: 9.8200

??

rock.freak667
Homework Helper
next: 9.8200
This is more or less correct.

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)

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!