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Homework Help: Vectors question

  1. Nov 16, 2015 #1
    NOTE: Thread was moved to Homework forums and thus has no homework template...

    7MHpMAN.jpg

    I managed to find (a) but i couldn't figure out (b).

    I think OR = OP + PR = (2/3)a + t( (-1/15)a + (2/5)b) but i don't know how to go further please guide or help me with this please. Thanks
     
  2. jcsd
  3. Nov 16, 2015 #2

    haruspex

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    There's a useful, directly observable, relationship between ##\vec{OR}## and b.
     
  4. Nov 16, 2015 #3
    Then i should just substitute t=10 into the OR= (2/3)a + t( (-1/15)a + (2/5)b) since the answer must be in terms of b. That would make it 4b.

    Is it correct?
     
  5. Nov 16, 2015 #4

    haruspex

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    Yes, but not because you are told the answer must be in terms of b. You know from the diagram that it must be in the direction of b. Unless a and b are in the same direction, how else will you get (2/3)a + t( (-1/15)a + (2/5)b) to be a scalar multiple of b?
     
  6. Nov 17, 2015 #5
    I completely understand now! Thanks!
     
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