jshark97
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Question 6 (b) from http://www.examsolutions.net/a-level...uary/paper.php

I watched the exam solutions solution, but I don't understand how it worked. Can anyone explain a different way of answering this, or just explain the theory...?
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Notnek
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(Original post by jshark97)
Question 6 (b) from http://www.examsolutions.net/a-level...uary/paper.php

I watched the exam solutions solution, but I don't understand how it worked. Can anyone explain a different way of answering this, or just explain the theory...?
The Examsolutions method is the way I would do it.

It would be useful if you tell us the exact part of the video where you first didn't understand something.
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Cryptokyo
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By adding both of the vectors you obtain 4i-5j+pi+qj=(p+4)i+(q-5)j
Since this vector is in the direction i-2j you obtain the expression
(p+4)i+(q-5)j=k(i-2j)
Where k is just a numerical value. As the force can be of greater magnitude than this vector. By splitting it into i and j components.
p+4=k
q-5=-2k
Sub one into other to get
q-5=-2(p+4)
so 2p+q+3=0
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Cryptokyo
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The theory is that the resultant force is found as the vector sum of all the forces acting upon a particle. If a direction is given for the resultant force then it will act in that direction but may be of a different magnitude hence the constant term k.
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