math vectors help
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Original post by brainmaster
ohhh yesyesyes. now?
So finding e in terms of i and j should be the same as for a except that P'E is in the -j direction where as P'A is in the j direction.
Original post by Dalek1099
So finding e in terms of i and j should be the same as for a except that P'E is in the -j direction where as P'A is in the j direction.
Why are you still persisting with this? Do you not realise that using i and j is needlessly complicating everything? In parts before the last part, only geometry is required (which should be evident from the fact that they are only worth a few marks), and in the last part, where it does become necessary to work algebraically, we can simply work with coefficients of a and e, since they are linearly independent. (Note that this is similar to how, in mechanics problems involving inclined planes, it's often much easier to resolve parallel and perpendicular to the slope, rather than rushing to always resolve horizontally and vertically).
(edited 5 years ago)
Original post by Dalek1099
So finding e in terms of i and j should be the same as for a except that P'E is in the -j direction where as P'A is in the j direction.
Yes so now e = |e| cos 60 i - |e| sin 60 j........now.how do we use this to get AB
Original post by brainmaster
Yes so now e = |e| cos 60 i - |e| sin 60 j........now.how do we use this to get AB
|e|=|a| Here and then add a+e and compare with AB=2|a|i.
Original post by Dalek1099
|e|=|a| Here and then add a+e and compare with AB=2|a|i.
As stated in post #42, none of this i and j crap is necessary for the first few parts of this question. Note also that in posts #4 and #9, ghostwalker, who is an extremely long-standing and respected member, provided a geometric solution, which the OP was happy with. I cannot fathom how someone can be so persistent as to keep on going with a demonstrably overcomplicated and inferior solution strategy for something that's only worth 2 marks.
Original post by Prasiortle
As stated in post #42, none of this i and j crap is necessary for the first few parts of this question. Note also that in posts #4 and #9, ghostwalker, who is an extremely long-standing and respected member, provided a geometric solution, which the OP was happy with. I cannot fathom how someone can be so persistent as to keep on going with a demonstrably overcomplicated and inferior solution strategy for something that's only worth 2 marks.
Yes it's true but I asked him to show me....I thought I could learn maybe a new method however I think you mentioned this earlier but he included unit vectors THANKS TO BOTH OF YOU. I really appreciate your time and effort
Original post by Dalek1099
|e|=|a| Here and then add a+e and compare with AB=2|a|i.
thanks alot...I got to learn something new....next time if I'm stuck I'll definitely have a try at this method! !!
Original post by Prasiortle
As stated in post #42, none of this i and j crap is necessary for the first few parts of this question. Note also that in posts #4 and #9, ghostwalker, who is an extremely long-standing and respected member, provided a geometric solution, which the OP was happy with. I cannot fathom how someone can be so persistent as to keep on going with a demonstrably overcomplicated and inferior solution strategy for something that's only worth 2 marks.
I often find that its useful for OP to know other methods to solve problems and I have recieved good feedback from previous OP's when I've posted a different method before. Had OP not replied to my comment then I wouldn't have replied back but OP seems to be interested in this method.
Original post by Dalek1099
I often find that its useful for OP to know other methods to solve problems and I have recieved good feedback from previous OP's when I've posted a different method before. Had OP not replied to my comment then I wouldn't have replied back but OP seems to be interested in this method.
Where there are various methods that are all equally good (e.g. differential equations that can be solved either using an integrating factor or using a complementary function/particular integral), then it's worth learning each of them, such that you have a variety of tools at your disposal. But when there's a quick geometric method as well as an algebraic method that's much more complicated, while the algebraic method may perhaps be interesting to consider, it's not necessary to learn/know it. As I said in my post #42, there are especially many examples of this in mechanics, not only with inclined planes but also with statics/equilibrium problems, where a geometric "triangle of forces" approach is much easier and more elegant than resolving everything into components (especially when some of the angles are unknown), and with e.g. relative velocity problems in which trying to work algebraically is doable in easier questions, but in harder questions (e.g. closest approach of two particles) gets very messy.
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