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Beads on Semi-Circular wire

 
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Jun20-12, 11:29 PM   #18

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Beads on Semi-Circular wire


Quote by Infinitum View Post
An easier approach is equating the velocities of A and B along the rod. Let the velocity of B be v, and then try to solve the problem.
It is ingenious, Infinitum!

My method is much more complicated.
The speed of the bead on the vertical line is dx/dt=u.
The speed of the bead on the circle is v=Rdβ/dt=Rω

From the cosine law in the tringle AOB,

[tex]L^2=R^2+x^2+2Rxcos(\beta)[/tex]

With implicit differentiation,

[tex]0=x u+R u cos(\beta)-Rx\sin(\beta) ω[/tex]

isolating v=Rω

[tex]v=u\frac{(1+\frac{R}{x}cos(\beta))}{\sin(\beta)}[/tex]

Form the sine law, [tex]\frac{R}{x}=\frac{\sin(\alpha)}{\sin(\beta-\alpha)}[/tex]

Plugging in and simplifying, we get:

[tex]v=u\frac{cos(\alpha)}{\sin(\beta-\alpha)}[/tex]

ehild
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Jun21-12, 01:01 AM   #19
 
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Quote by ehild View Post
The speed of the bead on the vertical line is dx/dt=u.
The speed of the bead on the circle is v=Rdβ/dt=Rω

From the cosine law in the tringle AOB,

[tex]L^2=R^2+x^2+2Rxcos(\beta)[/tex]

With implicit differentiation,

[tex]0=x u+R u cos(\beta)-Rx\sin(\beta) ω[/tex]

isolating v=Rω

[tex]v=u\frac{(1+\frac{R}{x}cos(\beta))}{\sin(\beta)}[/tex]

Form the sine law, [tex]\frac{R}{x}=\frac{\sin(\alpha)}{\sin(\beta-\alpha)}[/tex]

Plugging in and simplifying, we get:

[tex]v=u\frac{cos(\alpha)}{\sin(\beta-\alpha)}[/tex]

ehild
It's really complicated.
Thanks for an alternative solution.
 
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