Physics Help Forum If A = i + j + k and B = -I + -j + -k, then (A-B) will make angle with A?

 Kinematics and Dynamics Kinematics and Dynamics Physics Help Forum

Jul 17th 2018, 10:22 AM   #11
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 Originally Posted by studiot Indranil Note that 2 is a scalar. What happens to direction when you multiply (scalar * vector) ? Note that you asked for diagrams. I started to think about drawing htese like the last lot but you demonstrated some ability with algebra. The foregoing discussion shows how much easier algebra is in this 3 dimensional case. Do you still want diagrams ar can you now draw your own? One thing you suggested when I asked what A, B and (A-B) are was that they are unit vectors. Do you still think this or can you see why none of them are unit vectors?
NO

Jul 17th 2018, 10:24 AM   #12
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 Originally Posted by HallsofIvy Good. Notice that, since B= -A, A- B= A- (-A)= 2A. So what is the angle between A and 2A?
A and 2A cannot make any angle because they are parallel.

 Jul 17th 2018, 11:49 AM #13 Senior Member   Join Date: Apr 2015 Location: Somerset, England Posts: 1,035 No to which question? English is not your first language. Are you using Google translate or do you understand English?
 Jul 17th 2018, 03:07 PM #14 Senior Member     Join Date: Jun 2016 Location: England Posts: 850 A unit vector has Magnitude 1 By convention the letters i, j, and k are used to describe 3 unit vectors that are each at right angles to each other. I am assuming that the person who set your question is using this convention. If you go one unit in the i direction, then one unit in the j direction, then one unit in the k direction, then draw a line from the start position to the end position, This line will represent the vector A. The length of this line will be the Magnitude of A. Using Pythagoras (square root of the sum of the squares of the sides) will show that the Magnitude of A will not be greater than 1 Similarly for B (but in the opposite direction). __________________ ~\o/~
Jul 17th 2018, 04:35 PM   #15
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 will show that the Magnitude of A will not be greater than 1
Woody are you sure you wouldn't like to reconsider this?

Jul 17th 2018, 09:43 PM   #16
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 Originally Posted by studiot No to which question? English is not your first language. Are you using Google translate or do you understand English?
You are right. English is not my first language but I understand English. I want to inform you that I am still in the process of learning English. Please don't ignore me If I don't understand you. Please let me know where I don't comprehend you. Please help me to learn Physics here. Thanking you.

 Jul 18th 2018, 12:48 AM #17 Senior Member     Join Date: Jun 2016 Location: England Posts: 850 oops Would be greater than one root(3) > 1 Thanks for the catch Studiot __________________ ~\o/~ Last edited by Woody; Jul 18th 2018 at 12:51 AM.
Jul 18th 2018, 01:51 AM   #18
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 Originally Posted by Indranil You are right. English is not my first language but I understand English. I want to inform you that I am still in the process of learning English. Please don't ignore me If I don't understand you. Please let me know where I don't comprehend you. Please help me to learn Physics here. Thanking you.
Sure.

Remember the more that you say (good English or Bad English)
the better you will get at English.

But if you say nothing we don't know what to think.

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