- #1
kq6up
- 368
- 13
Homework Statement
7.27 ** Consider a double Atwood machine constructed as follows: A mass 4m is suspended from a string that passes over a massless pulley on frictionless bearings. The other end of this string supports a second similar pulley, over which passes a second string supporting a mass of 3m at one end and m at the other. Using two suitable generalized coordinates, set up the Lagrangian and use the Lagrange equations to find the acceleration of the mass 4m when the system is released. Explain why the top pulley rotates even though it carries equal weights on each side.
Homework Equations
##\frac { \partial L }{ \partial q } =\frac { d }{ dt } \frac { \partial L }{ \partial \dot { q } } ##
The Attempt at a Solution
Looking at the solution I did all the steps after setting up the Lagrange e.q. correctly. My lagrange is incorrect, but I am not sure where I went awry. Could you folks give a hint?
Here is my Lagrange E.Q.:
##L=4m{ \dot { q } }_{ 1 }^{ 2 }+2m{ \dot { q } }_{ 2 }^{ 2 }-2m\dot { { q }_{ 1 } } \dot { { q }_{ 2 } } +2mg{ q }_{ 2 }##
edit: This is the resultant equation after I expanded all the terms and added cross terms. The algebra is good, the initial setup is different than what the solution manual had. However, I am having trouble seeing how our initial equations are not different equations stating the same problem. The SM yielded: ## L=4m{ \dot { q } }_{ 1 }^{ 2 }+2m{ \dot { q } }_{ 2 }^{ 2 }+2m\dot { { q }_{ 1 } } \dot { { q }_{ 2 } } -2mg{ q }_{ 2 }## after the algebraic smoke cleared.
Thanks,
Chris
Last edited: