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Math Help - [SOLVED] Ahem, a bit of physics help here please guys...

  1. #1
    Bar0n janvdl's Avatar
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    [SOLVED] Ahem, a bit of physics help here please guys...

    No I don't have physics but I opened my big mouth saying it's easy stuff, and now I have to solve this thing... And returning without an answer is not an option...

    What are the components and length of a vector which is the sum of two vectors V1 and V2, whose components are (8.0; -3.7; 0.0) and (3.9; -8.1; 4.4) ?
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  2. #2
    Eater of Worlds
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    To find the sum of two vectors just add the components.

    (8,3.7,0)+(3.9,-8.1,4,4)=(11.9,-11.8,4.4)

    The length is the norm:

    \sqrt{(11.9)^{2}+(-11.8)^{2}+(4.4)^{2}}=\frac{\sqrt{30021}}{10}

    I reckon that is what you're after?.
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  3. #3
    Bar0n janvdl's Avatar
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    Quote Originally Posted by galactus View Post
    To find the sum of two vectors just add the components.

    (8,3.7,0)+(3.9,-8.1,4,4)=(11.9,-11.8,4.4)

    The length is the norm:

    \sqrt{(11.9)^{2}+(-11.8)^{2}+(4.4)^{2}}=\frac{\sqrt{30021}}{10}

    I reckon that is what you're after?.
    Galactus, I couldn't care less how to do it than just get the answer

    Thanks! (+rep+)
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  4. #4
    Super Member angel.white's Avatar
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    Physics is confusing -.^ Someone asked me a question the other day that was pretty straight forward (meaning I knew exactly what to do as soon as I heard it). But it involved gravity, so I went and looked gravity up, and it accellerates at like 9.8m/s^2 so I figured it's rate is -9.8m/s and distance is 9.8m ln|s|

    As I worked the problem, I quickly discovered this was not correct, and so I did some research and it states that 9.8m/s^2 is a constant. But why then does it have the time variable in it?!?! I don't know, I got pretty lost.

    Math > Physics anyway, so w/e.
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    Bar0n janvdl's Avatar
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    Quote Originally Posted by angel.white View Post
    Math > Physics anyway...
    It sure is! (Looks around nervously to see if Topsquark might have heard)
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    Quote Originally Posted by angel.white View Post
    Physics is confusing
    Because it is not well-defined, not formal, and other things. Math is. Therefore it is easier to understand exactly what the question is asking.
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    Forum Admin topsquark's Avatar
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    Quote Originally Posted by angel.white View Post
    Physics is confusing -.^ Someone asked me a question the other day that was pretty straight forward (meaning I knew exactly what to do as soon as I heard it). But it involved gravity, so I went and looked gravity up, and it accellerates at like 9.8m/s^2 so I figured it's rate is -9.8m/s and distance is 9.8m ln|s|

    As I worked the problem, I quickly discovered this was not correct, and so I did some research and it states that 9.8m/s^2 is a constant. But why then does it have the time variable in it?!?! I don't know, I got pretty lost.

    Math > Physics anyway, so w/e.
    Treat units as if they were constants. You won't get into trouble that way. So if an object has an acceleration of 9.8~m/s^2, then
    v = \int a~dt = 9.8t which has units of \frac{m}{s^2} \cdot s = m/s

    and
    s = \int v~dt = \frac{1}{2} \cdot 9.8t^2 which has units of \frac{m}{s^2} \cdot s^2 = m

    As to why acceleration has a time in it, it is simply the way the unit system is defined. We could easily develop a unit system where acceleration is in some new unit "accels" for example, which has no time reference, but then displacement would have the unit "accels" times seconds squared.

    -Dan
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    Forum Admin topsquark's Avatar
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    Quote Originally Posted by angel.white View Post
    Math > Physics anyway, so w/e.
    Quote Originally Posted by janvdl View Post
    It sure is! (Looks around nervously to see if Topsquark might have heard)
    No janvdl, I'm not upset about the comment. I expect such things from ignorant "mathemations" such as TPH etc.

    But look at it this way: Math does not use a unit system, but Physics does. And as primitive Math was being developed (ie. counting) it was done with a certain number of things, such as counting the number of apples in a basket. But the number of apples is a quantity with a unit attached! So Math owes it's origins to Physics.

    (Yes, yes I know. That argument is going to be swatted down pretty easily. But as this has little relevance to anything the original poster asked, we should probably continue this fruitless and pointless argument elsewhere.)

    -Dan
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    Quote Originally Posted by topsquark View Post
    I expect such things from ignorant "mathemations" such as TPH etc.
    I started to spell this word correct now.
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    Grand Panjandrum
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    Quote Originally Posted by janvdl View Post
    It sure is! (Looks around nervously to see if Topsquark might have heard)
    But your question was not physics, just a bit of vector manipulation.

    RonL
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  11. #11
    Super Member angel.white's Avatar
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    Quote Originally Posted by topsquark View Post
    Treat units as if they were constants. You won't get into trouble that way. So if an object has an acceleration of 9.8~m/s^2, then
    v = \int a~dt = 9.8t which has units of \frac{m}{s^2} \cdot s = m/s

    and
    s = \int v~dt = \frac{1}{2} \cdot 9.8t^2 which has units of \frac{m}{s^2} \cdot s^2 = m

    As to why acceleration has a time in it, it is simply the way the unit system is defined. We could easily develop a unit system where acceleration is in some new unit "accels" for example, which has no time reference, but then displacement would have the unit "accels" times seconds squared.

    -Dan
    That's weird, but thanks ^_^ I was kind of upset that it had me so confused. I think I eventually concluded that, but he never got back to me about whether my formulas were right. (I had to convert it to feet per second, though, so I don't remember exactly what my answer was).
    Quote Originally Posted by topsquark View Post
    No janvdl, I'm not upset about the comment. I expect such things from ignorant "mathemations" such as TPH etc.

    But look at it this way: Math does not use a unit system, but Physics does. And as primitive Math was being developed (ie. counting) it was done with a certain number of things, such as counting the number of apples in a basket. But the number of apples is a quantity with a unit attached! So Math owes it's origins to Physics.

    (Yes, yes I know. That argument is going to be swatted down pretty easily. But as this has little relevance to anything the original poster asked, we should probably continue this fruitless and pointless argument elsewhere.)

    -Dan
    Well I have a lot of respect for math, because after I lost my religion, I didn't believe that truth existed at all, whatsoever in any sense. While I still admit the possibility of anything, I have come to believe that there is almost for certain objective truths, and it is mostly mathematics which helped me to see this. That it is discoverable by anyone, and was discovered independently all over the world, and that it has such rigorous standards, and is tested billions of times a day without breaking down.

    So yeah, I'm biased for math, it seems so pure and beautiful to me because it is something that is true outside of each person, and because it isn't arbitrary, but is so logical to the point where you can anticipate how it will work if you understand it.

    I suppose physics has it's plusses too, it just seems that physics works because of math. Anyway, respect for physics people too probably if I spent some time with it, I wouldn't get frustrated.
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    Bar0n janvdl's Avatar
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    Quote Originally Posted by topsquark View Post
    No janvdl, I'm not upset about the comment. I expect such things from ignorant "mathemations" such as TPH etc.
    I guess it's also about personal taste. Some love maths, others love physics. I'm a maths guy though.

    Quote Originally Posted by CaptainBlack View Post
    But your question was not physics, just a bit of vector manipulation.
    Well it comes from a physics textbook... So i simply classified it as physics
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    I have come to believe that there is almost for certain objective truths, and it is mostly mathematics which helped me to see this. That it is discoverable by anyone, and was discovered independently all over the world, and that it has such rigorous standards, and is tested billions of times a day without breaking down.

    So yeah, I'm biased for math, it seems so pure and beautiful to me because it is something that is true outside of each person, and because it isn't arbitrary, but is so logical to the point where you can anticipate how it will work if you understand it.
    That is exactly why I chose math over physics.
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