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September 22, 2014

September 22, 2014

Posted by **Lindsay** on Saturday, December 15, 2007 at 10:45am.

I'm not sure how to solve these types of problems, given only mass and distance. Plus, the "in space" part sort of throws me off...

- Physics -
**drwls**, Saturday, December 15, 2007 at 11:10amThe "in space" part means there are no other objects around exerting forces on any of the spheres. I assume you know how to calculate the gravitational force between two bodies, with masses M1 and M2, using the Newtonian equation

F = G M1*M2/R^2

where 6.67 × 10^−11 N m2 kg-2 is the universal constant of gravity.

In this case, object 1 is pulled one way by object 2 and pulled other way by object 2. Compute the two forces and take the difference.

- Physics (correction) -
**drwls**, Saturday, December 15, 2007 at 11:11amchange that to "and pulled other way by object 3".

- Physics -
**bobpursley**, Saturday, December 15, 2007 at 11:13amThe īn space"means that the total gravitation effect is dependent on the spheres only.

Do this as vectors. Gravity is a vector, so the net force (to the right) is

Fnet= G*M1 ( - ml/.1060^2 + mr/.2070^2)

where M1 is 2.43kg, ml is 5.17kg, mr is 6.20 kg)

- Physics -
**Lindsay**, Saturday, December 15, 2007 at 12:04pmI tried both of the ways and got the same answer. However, the answer I got using bobpursley's equation got me -5.11E-8, when it was really positive. Was there an error in that equation, or did I just mess up with the math somewhere along the way?

- Physics -
**bobpursley**, Saturday, December 15, 2007 at 5:35pmPositive means the force is to the right, but looking at the numbers, it should be to the left (negative).

Yes, it is negative, I just put the numbers in the Google calculator, and it is definitely negative (to the left).

- Physics -
**Lindsay**, Sunday, December 16, 2007 at 9:29amOh ok I see. Well, my online homework site would only accept it as postive, but it has been known to make errors before.

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