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Math Help - Vectors

  1. #1
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    Vectors

    Electric point charges of magnitude 3,5 and 7 are placed at the points P(1,2,3) Q(2,3,4) and R(3,4,5) respectively. What is the magnitude and direction of the resultant force on a unit point charge placed at the point P(1,1,1)?. ( You may assume a single constant k to include electrical properties)
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  2. #2
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    Re: Vectors

    How far along are you? It might be difficult to draw a diagram of the problem because it is 3 dimensional, but you could start by setting up the vector sum:

    \overrightarrow F_{net}=\overrightarrow F_P+\overrightarrow F_Q+\overrightarrow F_R

    So you need to find each vector by finding the component of each vector. Have you tried this?
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  3. #3
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    Re: Vectors

    Yeah I have tried that. As we know the directions along which the forces act, I got the unit vector along each 3 directions and multiplied it by the magnitude of the force in order to get the 3 forces in vector form. And I think the resultant is the addition of the 3 vectors. But I'm having a confusion because they have included a 'k' saying "You may assume a single constant k to include electrical properties". How does this come into the answer?
    Any help would be great.
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  4. #4
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    Re: Vectors

    ?? If a charge, of magnitude 1, is at distance 1 from a charge of magnitude 2, what is the force between them? If you cannot answer that, how could you hope to answer the given question?
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  5. #5
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    Re: Vectors

    Please see whether I got that right this time.
    Electrostatic force between 2 particles is k(Q1Q2)/ r^2 .

    So, I can get the magnitudes of the forces by this as I know the magnitudes of the charges and the distance between them. Then I can get the unit vectors along the directions on which these forces act and multiply them by the force which I got from the equation above to get it in vector form. Then I can add the 3 vectors to get the resultant.
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  6. #6
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    Re: Vectors

    Quote Originally Posted by Kristen111111111111111111 View Post
    Please see whether I got that right this time.
    Electrostatic force between 2 particles is k(Q1Q2)/ r^2 .
    Yes, that's true (well, that the magnitude of the force vector- I assume that's what you meant). That's where the "k" came in!

    So, I can get the magnitudes of the forces by this as I know the magnitudes of the charges and the distance between them. Then I can get the unit vectors along the directions on which these forces act and multiply them by the force which I got from the equation above to get it in vector form. Then I can add the 3 vectors to get the resultant.
    Yes, that will work.
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