First off, I'm glad I found a forum like this! Thank jeebus!(adsbygoogle = window.adsbygoogle || []).push({});

I'm a new college physics student thats been out of the science/math arena for about 2.5 years. I'm a Software Engineer by day but I"m going back to get my mechanical engineering degree. Unfortunately I build business systems all day and physics nor calculus is used much in these applications that I build, hence why I'm kind of off the rocker on this stuff now.

I've been pouring over these problems ALL DAY LONG and I've beat my self up (mentally) because I cannot figure them out.

Just so you know, I'm not looking for the answer, I'm looking for the direction to go down to get hte answer. I want to learn this stuff as best as I can, but I need to know how it works!

With the introduction to the side, here I go...

In my physics book, I have a quesion that says:

"Newtons law of universal graviatation is represented by

F = GMm/r^2

HereFis the magnitude of the gravitational force exrted by one small object on another.Mamare the masses of the objects and r is a distance. Force has the SI units kg * m/s^2.

What are the SI units of the propotionally constantG? "

Here's what I've tried..

kg * m/s^2 = GMm/s^2

=> kg * m/L^2 = GMm/s^2

This is where my math skills are a little rusty. I know the dividing by a fraction is a little weird, but I think i remember how to do it. (I took Calc I and Calc II a couple years back, but like i said, I'm just rusty. As soon as I figure it out, I remember everything about it).

I'm not sure if it goes like this (which is how i've done it)

=> kg * s^2 = GMmm/r^2 => Gm^3/r^2

=> kg * s^2 = Gm^3/r^2

=> (kg * s^2)/G = m^3/r^2

=> 1/G = m^3 * (kg * s^2) / r^2 * 1

But this answer is COMPLETELY WRONG. I MEAN, WAY OFF... The answer is in the back of the book as:

m^3 / kg * s^2

I've tried moving around The G, replacing r^2 with L (length) and setting s^2 = L (lenth) and I've moved around fractions, numerators, demonminators, etc etc and I CANNOT get close to this answer at all.

What might I be doing wrong? TO tell you the truth, I"m not really sure what this quesiton is asking. Is it asking me to solve for G or what is it asking me to do? The question is under the section of dimensional analysis so i'm assuming that I need to make sure both sides are dimensionally correct. My answers never seem to add up!

I've tried thinking of all possibilities, solving for other variables, and I cannot wrap my head around this. The entire chapter never touches on anything like this at all.

Any help would be appreciated!

Thanks!

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# Homework Help: Dimensional Analysis Question

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