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    This question has been confusing me for at least a week :s I've got that K.E. = mgl(\cos \theta - \frac{1}{4}), but I don't see how that leads to the solution...

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    Any help is appreciated.
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    (Original post by jonatan18)
    This question has been confusing me for at least a week :s I've got that K.E. = mgl(\cos \theta - \frac{1}{4}), but I don't see how that leads to the solution...

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    Any help is appreciated.
    Then resolve inwards along the radius:
    T-mgcos theta=mv^2/l and substitute for v^2 from your KE
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    Is mv^2/l from circular motion? If so, why?
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    (Original post by jonatan18)
    Is mv^2/l from circular motion? If so, why?
    For circular motion, acceleration inwards along the radius is (v^2)/r or r(omega)^2
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    (Original post by tiny hobbit)
    For circular motion, acceleration inwards along the radius is (v^2)/r or r(omega)^2
    I'm still failing to see how this is an example of circular motion...
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    (Original post by jonatan18)
    I'm still failing to see how this is an example of circular motion...
    Try this out, physically. Tie something to the end of a piece of string, do as the question says and look at the path along which the object travels. It will be an arc of a circle.
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    (Original post by tiny hobbit)
    Try this out, physically. Tie something to the end of a piece of string, do as the question says and look at the path along which the object travels. It will be an arc of a circle.
    I thought circular motion was only true if the acceleration of the body is perpendicular to the motion. Where is this acceleration in this example?
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    (Original post by jonatan18)
    I thought circular motion was only true if the acceleration of the body is perpendicular to the motion. Where is this acceleration in this example?
    When a particle is moving in a vertical circle, there will also be acceleration along the tangent, but you never need to use it in M3.
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    (Original post by tiny hobbit)
    When a particle is moving in a vertical circle, there will also be acceleration along the tangent, but you never need to use it in M3.
    Is this a centrifugal acceleration?

    (BTW thanks a lot tiny hobbit; this has been a huge help with my understanding of mechanics)
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    (Original post by jonatan18)
    Is this a centrifugal acceleration?

    (BTW thanks a lot tiny hobbit; this has been a huge help with my understanding of mechanics)
    No, it's a tangential one.

    Centrifugal is a word associated with being flung outwards. There isn't a separate force/acceleration causing this. It's the feeling you get because you would carry on in a straight line if there were not an inwards force causing you to go round in a circle.
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    (Original post by tiny hobbit)
    No, it's a tangential one.

    Centrifugal is a word associated with being flung outwards. There isn't a separate force/acceleration causing this. It's the feeling you get because you would carry on in a straight line if there were not an inwards force causing you to go round in a circle.
    So does this mean that in a pendulum the acceleration can be described as either tangential or in the same plane as the displacement from the centre (\ddot{x}=-\omega^2 x)? If that's the case, how would I know which one would be appropriate for different problems?
 
 
 
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