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Homework Help: Physics homework PLEASE HELP i am lost

  1. Aug 30, 2007 #1
    i do not have a protractor with me and am very new to physics at the college level and have not gotten the book yet do to my student loans not bein processed and released at this time.... PLEASE HELP

    the question on my homework i am having trouble with is as follows

    go 83.9 paces at 188 degrees

    turn to 128 degrees and walk 199 paces

    then travel 73 paces at 179 degreess

    find the magnitude of the resultant displacement from the starting point, answer in units of paces.

    and what is the direction of the resultant displacement? use counterclockwise from due east as the positive angular direction between the limits of-180 degrees and +180 degrees. answer in units of degrees.
  2. jcsd
  3. Aug 30, 2007 #2
    you need to show work b4 help is given, but here is a thought: in what direction do we go when we speak of degrees, counter-clock or clock-wise?
  4. Aug 30, 2007 #3
    it does not say ... what i typed is word for word what the problem was.... im goin to assume counter clockwise from due east due to the last part of the last question

    if you can help me i would be ecstatic
  5. Aug 30, 2007 #4
    i dont even know how to begin this problem... this is my first physics course and i havent been able to get the book yet due to my student loans not coming in... i tried to diagram it out but i dont have a protractor so i couldnt get the angles right for the diagram method with scaling....

    and mathematically i am not sure of what procedure to even take

    im sorry i am totally lost in physics... this is the only problem i cannot figure out
  6. Aug 30, 2007 #5


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    Think of this as a math problem, not a physics one. Forget the protractor, think about creating a graph.
  7. Aug 30, 2007 #6
    i am tryin to make a graph but i cant figure out how to draw it correctly god i am such a moron right now.... i figure i need to do this.......

    x component ....

    a to b ..... 83.9 x cos(188) = number and what direction?

    b to c ..... 199 x cos (128) = number and what direction?

    c to d ...... 73 x cos(179) = number and what direction?

    i then add the numbers but the directions determine the +/- of the numbers

    i then do the same for the y components but with the sin of the angles

    and then i use those 2 final numbers to put into the pythagorean theorem?

    i just am not sure what directions the numbers are in in each component for each a to b, b to c and c to d

    and also am not sure becuz the cos of those angles = negative numbers

    am i close?

    please help me
  8. Aug 30, 2007 #7


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    Yes, you have basically figured it out.
    You're corrrect, those are negative numbers.
  9. Aug 30, 2007 #8
    but jeff if i use the cos of any of those angles it is a negative number? and how do i know what direction each is in?

    can u help me with that

    do i use cos for the x components and sin for the y components?

    and what directions is a to b? b to c? c to d?
  10. Aug 30, 2007 #9
    so all i really need is the directions to be correct then?

    if the cos of them is all negative wont my final answers be negative? does that even matter?
  11. Aug 30, 2007 #10


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    That was stated in the problem, a to b is direction 188 degrees, b to c is direction 128 degrees ...

    Try doing a simple example first:

    100 paces from the starting point, direction -90 degrees, where are you now? Next 100 paces from this point, +90 degrees, where are you now?

    Next example:

    100 paces, direction 0 degrees, then 100 paces +90 degrees, then 100 paces +180 degrees, then 100 paces 270 degrees.
  12. Aug 31, 2007 #11


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    No, it doesn't matter. It's ok to have negative movement.
  13. Aug 31, 2007 #12
    so for my problem would the directions be as follows?

    x component

    a to b = west
    b to c = east
    c to d = west

    y component

    a to b = south
    b to c = south
    c to d = north

  14. Aug 31, 2007 #13


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    Yes, you could combine a to b and call it south west.
  15. Aug 31, 2007 #14
    so if all my directions are correct

    i get for the x component

    a to b = -83.9 west
    b to c = -122.52 east
    c to d = -72.989
    x resultant = -34.36 west?

    and for the y component

    a to b = -11.68 south
    b to c = 156.81 south
    c to d = 1.27 north
    and the y resultant is 143.860 south?

    so then i square both and add them together? and then take the square root of that to get the first answer?
  16. Aug 31, 2007 #15
    jeff do u know the final answer to this problem... so that when i get an answer u can tell me if im right?
  17. Aug 31, 2007 #16
    would b to c be north west? and c to d for that matter?
  18. Aug 31, 2007 #17
    jeff u still here?
  19. Aug 31, 2007 #18


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    You don't need to worry about the directions for each part... just keep track of the numbers...

    83.9*cos(188) = -83.08... I just noticed that you had a different number.
  20. Aug 31, 2007 #19
    sodo i just add all those numbers up regardless of direction ? and just disregard the negative numbers and take them as positive numbers?

    i have entered 5 diff answers to my online class all are wrong?

    can u show me ur work if possible thanks

    what are the resultants for the x components and what are they for the y components?

    i have for the x components it is 279.409 and for the y components it is either 146.4 or 169.76????

    if these are wrong can u correct them and show me how u got the correct ones please

    please help... time is running out lol
    Last edited: Aug 31, 2007
  21. Aug 31, 2007 #20


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    When I add all the x-components I get: -278.589 paces

    When I add the y - components I get: 146.4115 paces

    The important thing to remember is that the signs take care of the direction... so don't worry about the direction till the end of the problem...

    Did you get these same numbers?
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