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anonymous

  • one year ago

would \[LT \left[ tu(t-30) \right]=\frac{ e ^{-30s} }{ s ^{2} }\] i'm not sure if applying the formula below would be right. \[LT \left[ u _{c}(t)f(t-c) \right]=e ^{-cs}F(s)\]

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  1. anonymous
    • one year ago
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    we know that \[LT \left[ u _{c}(t)=u(t-c) \right]=\frac{ e ^{-cs} }{ s }\]

  2. anonymous
    • one year ago
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    just from laplace tables

  3. anonymous
    • one year ago
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    ideas?

  4. anonymous
    • one year ago
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    Have you tried going through the integration?

  5. anonymous
    • one year ago
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    im unsure how to do that when we are considering u(t-30)

  6. anonymous
    • one year ago
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    Do you know how to work with the dirac delta function?

  7. anonymous
    • one year ago
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    not really, we just have a table of lapalce transforms used to help us in process control. my laplace transform is limited considering we weren't taught this in engineering maths yet it has come up in a third year topic which applies laplace transforms

  8. anonymous
    • one year ago
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    like, i start with the integral definition, \[LT(f(t)=\int\limits_{0}^{\infty}e ^{-st}tu(t-30)dt\]

  9. anonymous
    • one year ago
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    and try integration by parts...but i'm stuck with the t*u(t-30) bit, with applying the product rule on it

  10. anonymous
    • one year ago
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    Ok, so if you are using integration by parts, then you are considering this integral of the from\[\int\limits_{}^{}u dv = uv - \int\limits_{}^{}v du\]. What are you using as your u and your dv?

  11. dan815
    • one year ago
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    do a change of variables

  12. anonymous
    • one year ago
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    dv is the exponential and u is the t*u(t-30)

  13. anonymous
    • one year ago
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    ohh yea neat

  14. anonymous
    • one year ago
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    Thanks @dan815

  15. anonymous
    • one year ago
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    yeah nah that drawing has confused me lel

  16. dan815
    • one year ago
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    lol

  17. dan815
    • one year ago
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    i realized using s for the different variable was bad idea lol

  18. anonymous
    • one year ago
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    haha no joke i was gonna say

  19. dan815
    • one year ago
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    now u became the variable for laplace

  20. dan815
    • one year ago
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    lemme think so i wonder if we gotta add some extra stuff in for this shift

  21. anonymous
    • one year ago
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    could we just expand those brackets

  22. anonymous
    • one year ago
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    so instead of s lets use 'a' as our variable

  23. anonymous
    • one year ago
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    (a+30)u(a)= au(a)+30u(a)

  24. dan815
    • one year ago
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    its best to jst graph this stuff so we know for sure we dont have anything funky going on

  25. anonymous
    • one year ago
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    and laplacing these would be the same...

  26. anonymous
    • one year ago
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    where a=t-30

  27. dan815
    • one year ago
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    ohh something silly here oops

  28. dan815
    • one year ago
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    ont need to even worry about all this apprently

  29. anonymous
    • one year ago
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    lel

  30. dan815
    • one year ago
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    this is U_c(t) by definition

  31. anonymous
    • one year ago
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    yep

  32. anonymous
    • one year ago
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    but we can't use the formula thats on the top page cause it involves f(t-c) so here c=0 for the function f, but 30 for variable 'u'

  33. dan815
    • one year ago
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    |dw:1443326746594:dw|

  34. dan815
    • one year ago
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    i think what we did might be find, think abouut it like this, what is the laplace of this bottom graph

  35. dan815
    • one year ago
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    fine*

  36. anonymous
    • one year ago
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    just a ramp function, shifted from the origin..

  37. dan815
    • one year ago
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    u_30(t) * ((t-30)+30)

  38. dan815
    • one year ago
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    with this trick now we have a new function f(t)=t+30 and f(t-c)=f(t-30)=(t-30)+30

  39. dan815
    • one year ago
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    yay

  40. dan815
    • one year ago
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    |dw:1443326992420:dw|

  41. dan815
    • one year ago
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    |dw:1443327070058:dw|

  42. dan815
    • one year ago
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    this make sense?

  43. dan815
    • one year ago
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    |dw:1443327188716:dw|

  44. anonymous
    • one year ago
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    with the first and second step |dw:1443327215719:dw|

  45. dan815
    • one year ago
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    ya?

  46. anonymous
    • one year ago
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    should the first step be f(t-30)

  47. dan815
    • one year ago
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    no taht is what is figven

  48. dan815
    • one year ago
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    so i changed it to something that is f(t-30)

  49. anonymous
    • one year ago
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    |dw:1443327270524:dw|

  50. anonymous
    • one year ago
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    like what thats mean

  51. dan815
    • one year ago
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    (t)

  52. anonymous
    • one year ago
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    oh yea ns

  53. anonymous
    • one year ago
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    haha

  54. anonymous
    • one year ago
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    yeap sweet as man, cheers!

  55. dan815
    • one year ago
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    ok baby

  56. dan815
    • one year ago
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    greetings from Canada xD

  57. anonymous
    • one year ago
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    ur such a lad haha

  58. dan815
    • one year ago
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    lel

  59. anonymous
    • one year ago
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    still havent moved ay

  60. dan815
    • one year ago
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    how r things down in australia these days

  61. anonymous
    • one year ago
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    yea summer is coming, soo good. only like another 2 months then i'm in 4th yr.

  62. dan815
    • one year ago
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    truee yeee

  63. anonymous
    • one year ago
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    hopefully get a job and i'll be done yesss

  64. dan815
    • one year ago
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    good luck :)

  65. anonymous
    • one year ago
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    cheers man, hbu?

  66. dan815
    • one year ago
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    same story pretty much, gotta do capstone next year and land jobs

  67. anonymous
    • one year ago
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    wuts capstone?

  68. dan815
    • one year ago
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    itsd like this project every engineer has to do for final year, i think u too

  69. anonymous
    • one year ago
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    oh like research project

  70. dan815
    • one year ago
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    yeah

  71. anonymous
    • one year ago
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    yeah that will be aids

  72. dan815
    • one year ago
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    yeah its just htis one course that runs for the whole year and u have to work on it in your own time

  73. anonymous
    • one year ago
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    yeah thats our research project haha mine will focus more on mining but not sure what yet

  74. anonymous
    • one year ago
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    yolo

  75. dan815
    • one year ago
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    oh you decided already xD i still got no idea

  76. dan815
    • one year ago
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    ill probably do some detection stuff i just wanna write code and make my partners do the more circuit stuff

  77. anonymous
    • one year ago
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    my degree is focused in minerals processing/mining so its like i am forced to do something mining like haah yeah writing code sounds fun hahaha

  78. dan815
    • one year ago
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    cool

  79. dan815
    • one year ago
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    what kind engineering is that?

  80. anonymous
    • one year ago
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    chemical eng. so gai

  81. dan815
    • one year ago
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    oooo

  82. dan815
    • one year ago
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    chemistry is too hard -.-

  83. anonymous
    • one year ago
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    haha its pretty hectic but what i enjoy so its chill as.

  84. dan815
    • one year ago
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    u gotta actually learn like a lot of math to do real chem, but they dont teach all that math in a chem degree

  85. anonymous
    • one year ago
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    too many people will fail hahaha

  86. anonymous
    • one year ago
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    lots of science students aren't well educated in math anyway

  87. anonymous
    • one year ago
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    but enough of me speaking, i need some lunch! i'll let ya know how i go with this question after. cheers mate. peace

  88. dan815
    • one year ago
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    alright take care!!

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is replying to Can someone tell me what button the professor is hitting...

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