How Do You Calculate the Speed of Two Masses Attracting in Space?

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Homework Help Overview

The discussion revolves around calculating the speed of two masses, specifically baseballs, attracting each other in space due to their mutual gravitational attraction. The problem involves concepts from mechanics, particularly conservation of energy and momentum.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • The original poster attempts to apply the conservation of energy equation but expresses confusion about handling the masses involved. Some participants suggest that the kinetic energy should account for both masses and question whether the conservation of momentum has been considered.

Discussion Status

Participants are actively engaging with the problem, providing guidance on the correct application of conservation laws. There are multiple interpretations being explored, particularly regarding the treatment of kinetic energy and the necessity of considering momentum.

Contextual Notes

The original poster has indicated a specific distance change and has provided values for mass and gravitational constant, but there may be assumptions about the system's isolation and the effects of external forces that are not explicitly stated.

arydze2
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Two baseballs, each with a mass of 0.158 kg, are separated by a distance of 400 m in outer space. If the balls are released from rest, what speed do they have when their separation has decreased to 270 m? Ignore the gravitational effects from any other objects.
I keep on using the conservation of energy equation, but nothing seems to give, I feel like I'm missing a step, Please help...
This is what I've done so far
Ei=Ef
1/2mvi^2-(Gm1m2/ri)=1/2mvf^2-(Gm1m2/rf)
if this is the right equation...
KEi obviously = 0, how to I get rid of the mass(m) in the KEf, I can't cancel it out since there are 2 masses involved, am I right?
value for G = 6.67x10^-11
Thanks for the help.
 
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That is the right equation, except that the KE is the sum of the individual kinetic energies of the two balls. You also don't have to cancel out the mass (which is equal for both balls) since it is given.
 
Since you haven't mentioned it and said you feel like you are missing something (ie, maybe you have two velocities to solve for with one equation), don't forget conservation of momentum.
 
Yes,both total mechanical energy & momentum are conserved...Therefore they have the same speed in modulus...

Daniel.
 
arydzse2,

Yes, you're missing a step. Actually you're skipping it, and that's getting you confused.

Write the equations for total energy (both masses) before and after. Ei=? Ef=?
 

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