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phys
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Homework Statement
A point mass m is fixed inside a hollow cylinder of radius R, mass M and moment of inertia I = MR^2. The cylinder rolls without slipping
i) express the position (x2, y2) of the point mass in terms of the cylinders centre x. Choose x = 0 to be when the point mass is at the bottom.
Show the velocity of the point mass is:
x2' = x'(1-cos(x/R))
y2' = x'(sin(x/R))
ii) find the lagrangian for the generalised co-ordinate x
and write down the Euler lagrange equation to obtain the equation of motion for x (DO NOT SOLVE)
iii) find the frequency of small oscillations about the stable equilibrium state
Homework Equations
L = T-V
The Attempt at a Solution
i) can find this just by using the geometry of the situation and then differentiating
ii) I *think* the lagrangian is:
L = (x'^2)(M+m)(1-cos(x/R)) + mgRcos(x/R)
using the Euler lagrange equation I think the equation of motion is:
2x''(M+m)[1-cos(x/R)] - (x')^2((M+m)/R)(sin(x/R) + mgsin(x/R) = 0
iii) this is where I am stuck...
stable equilibrium is at x = 0
if you use sin x = x then the e.o.m reduces to:
2x''(M+m)(1-cos(x/R)) + mgx/R = 0
I have neglected the middle term since x/R^2 is negligible...
I was expecting to get an equation of the form x'' + w^2 x = 0 were w is the frequency ... however when expanding the cos you don't get this...
Have I done something really wrong?