Physics Help Forum The angle between P and Q?

 Kinematics and Dynamics Kinematics and Dynamics Physics Help Forum

 Jul 13th 2018, 08:33 AM #1 Junior Member   Join Date: Jul 2018 Posts: 17 The angle between P and Q? The resultant R of vectors P and Q is perpendicular to P and R=P both, then the angle between P and Q is what? Now, what is the concept behind it? Could you provide me with an image of the resultant perpendicular to two vectors so that I can understand the concept and start solving the problem?
 Jul 13th 2018, 09:29 AM #2 Physics Team     Join Date: Jun 2010 Location: Morristown, NJ USA Posts: 2,347 Please clarify what you mean by the phrase "R=P both" - are you trying to say that the magnitude of vector R = the magnitude of vector P? Keep in mind that for vector R (which is the sum of vectors P and Q) to be perpendicular to P, the vector Q must have a component in the negative P direction that is equal in magnitude to the magnitude of P, and Q must also have a component that is perpendicular to P. topsquark and Indranil like this.
Jul 13th 2018, 09:56 AM   #3
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 Originally Posted by ChipB Please clarify what you mean by the phrase "R=P both" - are you trying to say that the magnitude of vector R = the magnitude of vector P? Keep in mind that for vector R (which is the sum of vectors P and Q) to be perpendicular to P, the vector Q must have a component in the negative P direction that is equal in magnitude to the magnitude of P, and Q must also have a component that is perpendicular to P.
Could you please get your points a little bit easier with a diagram so that I can understand the concept well?

 Jul 13th 2018, 10:36 AM #4 Senior Member   Join Date: Apr 2015 Location: Somerset, England Posts: 1,035 Go back to you original definition of vector addition by the parallelogram law. Start by drawing vector P. From the same origin O, draw vector R the same length and at right angles to P. This will be the diagonal resultant of your parallelogram. Join the ends of the vectors R and P, noting the angle alpha as shown. Complete the parallelogram by drawing the vector OQ parallel to RP. Thus you can find the angle required by simple geometry. I will leave it to ChipB use these diagrams to explain what he means by components if he wants. Attached Thumbnails   topsquark and Indranil like this. Last edited by studiot; Jul 13th 2018 at 03:18 PM. Reason: spelling
Jul 13th 2018, 09:40 PM   #5
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 Originally Posted by studiot Go back to you original definition of vector addition by the parallelogram law. Start by drawing vector P. From the same origin O, draw vector R the same length and at right angles to P. This will be the diagonal resultant of your parallelogram. Join the ends of the vectors R and P, noting the angle alpha as shown. Complete the parallelogram by drawing the vector OQ parallel to RP. Thus you can find the angle required by simple geometry. I will leave it to ChipB use these diagrams to explain what he means by components if he wants.
Thanks a lot. So kind of you.

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