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Lagrangian mechanics(goldstein)

  • Thread starter Niishi
  • Start date
11
0
1. Homework Statement

A particle of mass m moves in one dimensional such that it has the Lagrangian

[itex] L=\frac{m^2\dot{x}^4}{12} + m\dot{x}^2V\left(x\right)- V^2\left(x\right) [/itex]

where V is some differentiable function of x only.
(i) Find the equation of motion for x(t)

(ii) Find an expression for the total energy and hence describe the physical nature of the system on the basis of this equation.


3. The Attempt at a Solution

[itex]
\frac{\partial{L}}{\partial{x}}= m\dot{x}^2\frac{dV}{dx}- 2V\frac{dV}{dx} [/itex]

[itex] \frac{d}{dt}\left(\frac{\partial{L}}{\partial{\dot{x}}}\right) = m^2\dot{x}^2 + 2mV\ddot{x} [/itex]

[itex] m\dot{x}^2\frac{dV}{dx}- 2V\frac{dV}{dx} - m^2\dot{x}^2\ddot{x} - 2mV\ddot{x} = 0 [/itex]

[itex] \frac{dV}{dx}\left(m\dot{x}^2-2V\right)- m\ddot{x}\left(m\dot{x}^2 +2V\right) =0 [/itex]
1. Homework Statement



2. Homework Equations



3. The Attempt at a Solution
 

Answers and Replies

pam
455
1
In your second line, m^2xdot^2 is wrong.
You took the d/dt wrongly.
 

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