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Finding mass of speaker?

  1. Mar 20, 2014 #1
    1. The problem statement, all variables and given/known data
    A speakerh angs from the ceiling by a pair of wires, as showin the diagram below. the tension in wire 1 is 35N. What is the mass of the speaker?
    Given from the problem and picture.


    Wire1=25 degrees
    Wire2=55 degrees
    Tension in wire1= 35N
    Tension in wire2=18.02N

    2. Relevant equations
    F=ma
    x=T1sin(x)-T2sin(x)


    3. The attempt at a solution
    This is what I got but didn't get full points becasue I am missing the Y component?

    x=35sin(25)-T2sin(55)
    T2=35sin(25)/sin55
    T2=18.05

    Then we used this equation
    T1y+T2y-mg
    0=T1y+t2y-m(9.8)
    Rearange and plug in numbers:
    35+18.05/9.8

    m=5.41kg

    She told me I am right all the way up to the last part (35+18.05/9.8) and was told I'm need the y-components..but I solved for it?

    Thank you!
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Mar 20, 2014 #2

    Simon Bridge

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    You didn't use the y components.

    You have m= (T1y+T2y)/g = (35+18.05)/9.8

    i.e. T1y=35N

    but are you not told that T1=35N ?
    if T1y=35N as well then T1x=0N - does that make sense?
     
  4. Mar 20, 2014 #3
    So i need to find my x-components of T2x and then have both sides equal to each other?
    But if T1x=0n then that is not relative to the equation?
    Sorry for the questions, I"m still a bit confused.
     
  5. Mar 20, 2014 #4

    Simon Bridge

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    You need both x and y components.

    Draw a free body diagram for the speaker.
    Divide the forces (tensions) into components parallel and perpendicular to gravity (easiest approach).
    The horizontal forces sum to zero.
    The vertical forces sum to zero.

    You should end up with two equations and two unknowns.

    Note:
    if T1x=0 then there is no x component: what direction must T1 be acting in?
    Does that fit the description?
     
  6. Mar 21, 2014 #5
    so I would have to do instead of sin, I have to use cos?

    35cos(25)/cos(55)= 55.30
     
  7. Mar 22, 2014 #6

    Simon Bridge

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    You should use your understanding of trigonometry and vectors to solve the problem.
    In long answers, you should show your understanding by what you write.

    What you wrote in post #5 reads like you have just randomly guessed that you need to change all the sines to cosines as if you have not understood anything that has been suggested before.

    If you won't take suggestions, I cannot help you.
    If you don't answer questions, I cannot help you.
     
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