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m3- springs Watch

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    Hi

    I've posted the question and the solution from the book.

    I don't understand why it's 2g - T and not T - 2g

    Thanks
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    (Original post by maggiehodgson)
    Hi

    I've posted the question and the solution from the book.

    I don't understand why it's 2g - T and not T - 2g

    Thanks
    the direction of x increasing is "downwards"
    hence the direction of x double dot must also be downwards
    So this is the "positive direction", so 2g - T
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    (Original post by maggiehodgson)
    Hi

    I've posted the question and the solution from the book.

    I don't understand why it's 2g - T and not T - 2g

    Thanks
    By Newton II, the nett force vector causes an acceleration vector that points in the same direction as the nett force vector. Here acceleration is +ve downwards, so we have to add up the force vectors taking that convention into account i.e. 2g is a +ve force, since it points downwards, T is a -ve force, as it points upward.

    So we have 2g + (-T) = ma

    To make this clear to yourself when solving 1D mechanics problems, you should make sure to:

    1) draw a picture labelling the all of the force arrows
    2) draw an arrow, labelled "+ve" pointing in the direction you choose as +ve
    3) Add up the force vectors according to that convention
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    Sorry for the delay in reply. I've been working on it trying to make sense of what I was doing (I'm a bit slow on the uptake with mechanics).

    I've done something that seems to turn out OK but I would appreciate it if you would check my logic.

    Thanks
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    (Original post by TeeEm)
    the direction of x increasing is "downwards"
    hence the direction of x double dot must also be downwards
    So this is the "positive direction", so 2g - T
    Yes. I think I might have got it now.

    Thanks
 
 
 
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