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woleraymond Group Title

The resultant of vectors A and B has a magnitude of 20units. A has a magnitude of 8units and the angle between A and B is 40 degrees. calculate the magnitude of B?

  • 2 years ago
  • 2 years ago

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  1. rs32623 Group Title
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    \[(8^{2}+B^{2}+2*8*B*Cos40)=20^{2}\] Can you proceed from here finding the value of B?

    • 2 years ago
  2. Vincent-Lyon.Fr Group Title
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    Use ruler and compass. You will get the value you need, then use geometry. Either resolve your vectors or work out magnitude directly using following link: http://en.wikipedia.org/wiki/Law_of_cosines

    • 2 years ago
  3. woleraymond Group Title
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    @rs32623 which formula are u using?

    • 2 years ago
  4. Vincent-Lyon.Fr Group Title
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    He is using the Law of cosines I mentioned above.

    • 2 years ago
  5. rs32623 Group Title
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    i am using the formula for the resultant of two vectors A & B having magnitude A & B & angle between them if theta then the resultant is R=sqrt(A^2+B^2+2*A*B*Costheta)

    • 2 years ago
  6. woleraymond Group Title
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    i think the preferred solution is Resultant = \[sqrt{A^2 + B^2}\]

    • 2 years ago
  7. Vincent-Lyon.Fr Group Title
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    But this is true if and only if vectors A and B are at right angles.

    • 2 years ago
  8. woleraymond Group Title
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    if it is cosine rule then it should be R=sqrt(A^2+B^2-2*A*B*Costheta)....do you guys agree....@Vincent-Lyon.Fr @rs32623

    • 2 years ago
  9. Vincent-Lyon.Fr Group Title
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    You should end up with B = 13.20

    • 2 years ago
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