# Gravitational Attraction

Redbelly98
Staff Emeritus
Homework Helper
You're not far off. Something went awry when you plugged in the numbers, but you are close.

man big numbers frustrate me, i didnt even round so that id get a better answer but okay so here are my numbers:
mE: 5.98x10^24 kg
mM: 7.35x10^22 kg
R: 3.84x10^8 m

= 2(5.98x10^24)(3.84x10^8) +/- { 4(7.35x10^22)(5.98x10^24)(3.84x10^8)} /
2(5.98x10^24) - 2(7.35x10^22)

= 4.6x10^33 +/- {6.8x10^56} / 1.2x10^25

= 4.6x10^33 / 1.2x10^25

= 3.8x10^8

**i rounded the numbers i wrote here just to write less, but i plugged in complete numbers into the calculator

okay scrap that lol, i tried it a completely different way:

dE = {mE}(R) / {mM}+{mE}

= 3.457x10^8 m

** which sounds more reasonable as an answer

okay scrap that lol, i tried it a completely different way:

dE = {mE}(R) / {mM}+{mE}

= 3.457x10^8 m

** which sounds more reasonable as an answer
According to your equation dE = 3.79*10^8 wich is much too close to the moon.

$$\frac {2 m_e R \pm \sqrt {4 m_e m_m R^2}} { 2m_e - 2m_m}$$

this is really correct. You can still cancel a 2 and get R^2 out from under the square root sign. I hope you do not do the algebra in ascii, but write it out on paper.

A calculator that does variables is very useful. It's much harder to make mistakes if
you can enter:

>>> me = 5.98e24
>>> mm = 7.35e22
>>> R = 3.84e8
>>> me*R/(mm+me)
379337573.30469972

(this is in python)

Redbelly98
Staff Emeritus
Homework Helper
= 2(5.98x10^24)(3.84x10^8) +/- { 4(7.35x10^22)(5.98x10^24)(3.84x10^8)} /
2(5.98x10^24) - 2(7.35x10^22)

= 4.6x10^33 +/- {6.8x10^56} / 1.2x10^25
Here you forgot to square R inside the square root { } expression. It should be
(3.84x10^8)^2

Anyway, you got it to work out (perhaps by reading the other thread with this same problem).

p.s. Note to kammerling: he is using { } to signify square rooots.

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