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Thread: Can anyone help me in this question

  1. #1 Can anyone help me in this question 
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    I'm currently confused in pulley system and lift system.can anyone here explain to me?
    thx


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  3. #2  
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    http://en.wikipedia.org/wiki/Pulley


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  5. #4  
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    Erm..thats not what i want...erm...im from malaysia taking science stream currently...can anyone tell me is there any book that suits me?
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  6. #5 Re: Can anyone help me in this question 
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    Quote Originally Posted by cheenaik
    I'm currently confused in pulley system and lift system.can anyone here explain to me?
    thx
    I think you gave us insufficent information, for a proper answer.
    Why dont you mention the part of pulley concept which you did'nt understand proprely.
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  7. #6  
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    OK....the question sounds like this:Two weight of mass 2 kg and 3kg are joined by a length of rope which passes over a smooth pully as shown above.If the system is released from rest,what is the acceleration of the 3 kg weight....what i dont understand is why when we are calculating the acceleration why we dont count in the mass of the 2 kg? and there is a question...a ball is thrown vertically until a max height is reached..it takes 1 second to do that...and when it falls down....will the ball take 1 second to do that?if yes why?
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  8. #7  
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    Oops ...forget to tell that..the diagram is a pully with a rope on and the two ends are connected with objects have weight 2kg and 3 kg respectively
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  9. #8  
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    gravity is causing the acceleration and is independant of mass. so whatever the mass be, the acceleration acquired is same
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  10. #9  
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    Um, what solution do you have?

    Lets suppose we have two weights m<sub>1</sub> and m<sub>2</sub> connected by a length of unstretchable, massless rope through a perfect pulley. if m<sub>1</sub> < m<sub>2</sub> we obtain the equations

    m<sub>1</sub> a = T - m<sub>1</sub> g
    m<sub>2</sub> (-a) = T - m<sub>2</sub> g

    where a is the acceleration of the masses (positive is the up direction) which must have the same magnitude if the rope is massless and cannot stretch (else it would support an unbalanced force due to unequal tensions T in a rope with no mass which results in infinite acceleration of a piece of rope!)

    we can solve for a here quite quickly to obtain

    a = (m<sub>2</sub> - m<sub>1</sub>) / (m<sub>2</sub> + m<sub>1</sub>)

    So the acceleration clearly depends on both masses.

    For your second question, the answer is yes if you ignore air friction - look at the equation for the balls motion (what curve is that and what are the relationships between the distance of its zero's and turning point) to see why.
    As is often the case with technical subjects we are presented with an unfortunate choice: an explanation that is accurate but incomprehensible, or comprehensible but wrong.
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  11. #10  
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    F=ma

    and a force diagram is all you need.

    (oh and the acceleration due to gravity is about 10m/s^2 at Earth's surface)
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