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M1 Vectors Question (last minute)

Question 7 (c) (ii) here http://www.examsolutions.net/a-level-maths-papers/Edexcel/Mechanics/Mechanics-M1/2011-June/paper.php#Q7

I did a triangle just like in exams solution's video, but to find the length of the base of the triangle I minused Q's x coordinate from P's x coordinate to give: 3t-(1+2t) = t-1. This doesn't work and I don't really understand why, could anyone explain?
Original post by jshark97
Question 7 (c) (ii) here http://www.examsolutions.net/a-level-maths-papers/Edexcel/Mechanics/Mechanics-M1/2011-June/paper.php#Q7

I did a triangle just like in exams solution's video, but to find the length of the base of the triangle I minused Q's x coordinate from P's x coordinate to give: 3t-(1+2t) = t-1. This doesn't work and I don't really understand why, could anyone explain?


use your answer from part b iii) when north west, the i component will be -m and the j component will b m

set the i part of part b iii) to -m and j part of part biii) to m and solve to find t
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jshark97
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Original post by KloppOClock
use your answer from part b iii) when north west, the i component will be -m and the j component will b m

set the i part of part b iii) to -m and j part of part biii) to m and solve to find t
That makes sense on its own, but I still don't understand what is wrong with the logic of minusing the coordinates of P's from Q's to find the difference, could you explain..? Sorry if being a bit awkward, I just don't see why it went wrong
(edited 7 years ago)
Original post by jshark97
That makes sense on its own, but I still don't understand what is wrong with the logic of minusing the coordinates of Q's from X's to find the difference, could you explain..? Sorry if being a bit awkward, I just don't see why it went wrong


minusing P from Q is what you did in part b iii anyway???? and then you use that with -i + j to find the time
(edited 7 years ago)
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Original post by KloppOClock
honestly im not too sure what you mean by that, ive always just known that northwest means m(-i + j) and used that to solve it. never used the triangle method or what you did. ask a teach or tag someone like zacken maybe!
Uh how do I tag?
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jshark97
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Original post by KloppOClock
minusing P from Q is what you did in part b iii anyway???? and then you use that with -i + j to find the time
I haven't learned your method of making the i component negative, I just saw it as Q has x coordinates (3t) and P has x coordinates (1+2t), therefore the length between these points should be (3t)-(1+2t), but it isn't...
Original post by jshark97
Uh how do I tag?


tagged
Original post by jshark97
I haven't learned your method of making the i component negative, I just saw it as Q has x coordinates (3t) and P has x coordinates (1+2t), therefore the length between these points should be (3t)-(1+2t), but it isn't...


no thats right, you get t-1 for the i component. do the same for the j component and you get 7t-3

set the i equal to -m as the i=j except as northwest the i will be negative
set the j equal to m
solve for t
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jshark97
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Original post by KloppOClock
no thats right, you get t-1 for the i component. do the same for the j component and you get 7t-3

set the i equal to -m as the i=j except as northwest the i will be negative
set the j equal to m
solve for t
I think I sort of understand, if that type of question comes up I'll remember what you said. Thanks for helping me at such a late time, really appreciated :smile:
Original post by jshark97
I think I sort of understand, if that type of question comes up I'll remember what you said. Thanks for helping me at such a late time, really appreciated :smile:


no problem, good luck

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