Physicists/Math Gurus - need your help (re-posting)?

2014-08-19 6:10 pm
Re-posting in hope of getting some numbers (I realize I will need two numbers for R in order to get two different Forces)..
I am creating a puzzle based upon Newton's Law of Universal Gravitation (F= G((m1 x m2)/r squared) I am trying to work backwards so that F gives me two pre-selected numbers: 4328804 and 11201129. If we assume the mass of the two objects are 45.3592kg and 56.600kg respectively (converted 100lbs and 125lbs to kg) I get the result of 2571.8212808. So that should be decided by the distance between them squared. The result should be multiplied by G to get my desired results. But for the life of me, I can't work it backwards to find the value of the distance needed to get each desired result (I seem to come close, but off). I have been using an on-line scientific calculator so maybe the limitations there is screwing me up. Just as an FYI - I am making a puzzle and the results should be North and West coordinates. (geocaching thing). Thanks for your help.....I'll post the link to the puzzle when I am done and thank you in it (your user name unless you tell me different). Newton's Formula: http://csep10.phys.utk.edu/astr161/lect/history/gravity.gif
更新1:

For the first one, I did this: (2571.8212808/rsquared) * G = 4328804 So, then 2571.8212808/rsquared = 4328804/G. Which gave me: 2571.8212808/rsquared = 64857992172938510. So I then thought Rsquared = 2571.8212808 / 6485799217293851 so R would be the square root of: 0.0000000000000396500000010359293504 with r being= 0.00000019912307752. Is my math wrong (it has been nearly 30 years since I took algebra). In any event, would love some help determining what two values for "R" I need. Thanks!!!!

回答 (2)

2014-08-20 12:34 am
✔ 最佳答案
Your calculation is spot on. I would suggest to plug in the values at one go instead of making individual calculations.

F = 4328804 N
m1= 100 lbs
m2 = 125 lbs
G = 6.674 x 10^-11 N m²/Kg²
r = ?

F = G(m₁x m₂)/r²
r² = G(m₁x m₂)/F
r = √[G(m₁x m₂)/F]
r = √[6.674 x 10^-11 x (110 x 0.45359237) x (125 x 0.45359237) / 4328804]
r = 0.000000208846033 m
r = 2.08846033 x 10^-7 m
r = 2.08846033 x 10^-7 m x (10^9 nm / 1m) = 208.846033 nm

Similarly for F = 11201129
r = √[6.674 x 10^-11 x (110 x 0.45359237) x (125 x 0.45359237) / 11201129]
r = 0.000000129831266 m
r = 1.29831266 x 10^-7 m
r = 1.29831266 x 10^-7 m x (10^9 nm / 1m) = 129.831266 nm
2014-08-20 3:39 am
Thank you!!!! This is the help I needed.


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