Momentum Problem: Jack and Jill on a Crate

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SUMMARY

The discussion centers on a physics problem involving Jack and Jill jumping off a crate on a frictionless surface. The key equation derived is the conservation of momentum, expressed as m1v + m2v + mVc = 0, leading to the formula for the crate's final speed, Vc = (m1v + m2v) / (-m). The user expresses uncertainty about whether to apply momentum conservation or energy conservation, highlighting the importance of understanding when each principle is applicable in physics problems.

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  • Understanding of classical mechanics principles, specifically momentum conservation.
  • Familiarity with the concept of mass and velocity in physics.
  • Knowledge of equations of motion in a frictionless environment.
  • Ability to differentiate between momentum and energy conservation laws.
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Homework Statement


Jack and Jill are standing on a crate at rest on the frictionless, horizontal surface of a frozen pond. Jack has a mass of m1, Jill has a mass of m2, and the crate has a mass of m. They remember that they must fetch a pail of water, so each jumps horizontally from the top of the crate. Just after each jumps, that person is moving away from the crate with a speed of v relative to the crate. What is the the final speed of the crate if jack and jill jump off the crate simoltaneously in the same direction.


Homework Equations




The Attempt at a Solution



I know that this has something to do with momentum

I solved the total momentum of the system equal to zero and solved for the v of the crate Vc.

m1v+m2v+mVc=o and solved for Vc to get

Vc=(m1v+m2v)/(-m)

This is incorrect. I don't really know if I should be using momentum or conservation of energy in this problem. thanks for all your help.
 
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which conservation to use? well, when does each apply?
 

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