Multivariable DE and Momentum Problem

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SUMMARY

The discussion focuses on a momentum problem involving a varying mass, specifically where the rate of mass change (dm/dt) is greater than zero, and incorporates air resistance modeled by Stokes' law. The equation derived is 6πnRv - mg(1 - p(water)/p(object)) = m (d/dt(v)) + v (d/dt(m)). The participant expresses difficulty in separating variables to solve the equation, highlighting the challenge of having a single equation with two dependent variables, which is insufficient for finding a unique solution.

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  • Understanding of Newton's laws of motion
  • Familiarity with Stokes' law and its application in fluid dynamics
  • Knowledge of multivariable calculus, particularly in relation to differential equations
  • Basic principles of momentum and mass flow in physics
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  • Study the separation of variables technique in differential equations
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jesusfreak324
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Ok, so I am doing a typical momentum problem with a varying mass (here dm/dt > 0). I am also taking into account air resistance (stoke's law essentially). After some manipulations I basically get:

6πnRv - mg(1 - p(water)/p(object)) = m (d/dt(v)) + v (d/dt(m))

I know I need to separate the variables but I am lost on how. Thank you for the assistance!
 
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jesusfreak324 said:
Ok, so I am doing a typical momentum problem with a varying mass (here dm/dt > 0). I am also taking into account air resistance (stoke's law essentially). After some manipulations I basically get:

6πnRv - mg(1 - p(water)/p(object)) = m (d/dt(v)) + v (d/dt(m))

I know I need to separate the variables but I am lost on how. Thank you for the assistance!
With only a single equation in two dependent variables, you can't. Just as you cannot solve a single equation for two unknowns.
 

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