Physics Help Forum Vector magnitude

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 Jul 15th 2019, 10:46 AM #1 Junior Member   Join Date: Jul 2018 Posts: 22 Vector magnitude Two forces, each equal to P, act at right angles. Their effect may be neutralized by a third force acting along their bisector in the opposite direction with a magnitude of___________ in this diagram, the resultant vector is the opposite direction, So what should I do the addition of vector or subtraction of vector? I am confused. Attached Thumbnails
Jul 15th 2019, 11:59 AM   #2
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 Originally Posted by Indranil Two forces, each equal to P, act at right angles. Their effect may be neutralized by a third force acting along their bisector in the opposite direction with a magnitude of___________ in this diagram, the resultant vector is the opposite direction, So what should I do the addition of vector or subtraction of vector? I am confused.
You certainly want to add the two given vectors, That is what the "effect" or two vectors means! Calling this "third vector" Q, We have P+ P+ Q= 0 (that's what "neutralized" means) so Q= -2P.

We can, without loss of generality, take the x and y axes in the directions of the two vectors. Then you can write the two vectors as <P, 0> and <0, P>. They sum to <P, P> which has magnitude $P\sqrt{2}$. The "third force" is the opposite of that <-P, -P> which also has magnitude $P\sqrt{2}$.

Last edited by HallsofIvy; Jul 15th 2019 at 12:04 PM.

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