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    How do I get my equations when given a diagram for example:

    You have 2 spherical objects on a light inextensible string (on the peg). Then, the string on one side goes downwards on one side.. How do I get the equations the right way round?

    Cos usually one is -T in one equation and the other is usually +T?
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    the one which is going to move down will have a larger mg than T... so put -T
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    (Original post by MKaur18)
    How do I get my equations when given a diagram for example:

    You have 2 spherical objects on a light inextensible string (on the peg). Then, the string on one side goes downwards on one side.. How do I get the equations the right way round?

    Cos usually one is -T in one equation and the other is usually +T?
    Can you give an example? Are we talking about connected particles?

    We use F=ma on both, one particle is moving down so

    Mg - T = Ma because the weight is pulling it down

    On the lighter particle the tension is pulling it up

    T - mg = ma

    Is this what you mean?
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    (Original post by Muttley79)
    Can you give an example? Are we talking about connected particles?

    We use F=ma on both, one particle is moving down so

    Mg - T = Ma because the weight is pulling it down

    On the lighter particle the tension is pulling it up

    T - mg = ma

    Is this what you mean?
    Yes. Right ok, thanks. Did you memorise that then apply it to questions? Cos, I did it a while ago, and forgot how to approach those questions.. :O oops.

    (Original post by the bear)
    the one which is going to move down will have a larger mg than T... so put -T
    Ok.
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    (Original post by MKaur18)
    Yes. Right ok, thanks. Did you memorise that then apply it to questions? Cos, I did it a while ago, and forgot how to approach those questions.. :O oops.



    Ok.
    No, I get students to draw a diagram, decide which one is moving down, add an arrow to show that and call acceleration 'a'.

    Then explain: using F = ma on particle A gives ....
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    (Original post by Muttley79)
    No, I get students to draw a diagram, decide which one is moving down, add an arrow to show that and call acceleration 'a'.

    Then explain: using F = ma on particle A gives ....
    After drawing the diagrams, I struggle to figure if T is negative.. but I think I've got it.

    T is negative on the one going downwards (heavier one).
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    (Original post by MKaur18)
    After drawing the diagrams, I struggle to figure if T is negative.. but I think I've got it.

    T is negative on the one going downwards (heavier one).
    Yes, the weight of the heavier one is pulling the system down and the tension in the string is acting against gravity. A diagram with forces marked on it really helps.
 
 
 
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