Author Topic: annoying vectors question!! (Read 1164 times) Tweet Share

Nato · « **on:** November 25, 2012, 02:45:01 pm »

hey everyone

i have a attached a vectors question which i am reeeaaallly stuck on, any help would be greatly appreciated.
in particular, i need help which question "b" and "c"

thank you

polar · « **Reply #1 on:** November 25, 2012, 03:01:25 pm »

(b)
$\begin{aligned}\vec{AP} &= 2\vec{PB} \\ \text{so, \;} \vec{AB} &= 3\vec{PB} \\ \vec{PB} &= \frac{1}{3}\vec{AB} \\ &= \frac{1}{3}(\bold{b}-\bold{a})\end{aligned}$

(c)
$\begin{aligned} \vec{AP} &= 2\vec{PB} \\ \vec{OP} - \vec{OA} &= 2(\vec{OB} - \vec{OP}) \\ \vec{OP} + 2\vec{OP} &= \vec{OA} + 2\vec{OB} \\ 3\vec{OP} &= \vec{OA} + 2\vec{OB} \\ \vec{OP} &= \frac{1}{3}(\bold{a} + 2\bold{b}) \end{aligned}$

Nato · « **Reply #2 on:** November 25, 2012, 03:08:16 pm »

thanks i understand (b), but could you please clarify your working for (c)?

polar · « **Reply #3 on:** November 25, 2012, 03:16:23 pm »

the question stated that $\vec{AP} = 2\vec{PB}$ , the vector joining point A to point P can be found by evaluating $\vec{OP} - \vec{OA}$ , similarly, $\vec{PB} = \vec{OB} - \vec{OP}$ , using these you can go backwards to find everything in terms of OA, OB and OP to solve for OP

Nato · « **Reply #4 on:** November 25, 2012, 03:32:26 pm »

crystal clear now, thanks man

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Author Topic: annoying vectors question!! (Read 1164 times) Tweet Share

Nato

annoying vectors question!!

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Nato

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polar

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Nato

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