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Physics question, solved but need clarification

  1. Mar 3, 2009 #1

    RS7

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    Physics question, solved but need clarification!!

    1. The problem statement, all variables and given/known data
    A bird take 8.5 s to fly from position A to position B. Determine the bird's avg acceleration
    Vb = 7.8 m/s [25 degrees N of E]
    Va = 4.4 m/s [ 31 degrees S of E]


    2. Relevant equations
    Vax/Va = cos31
    Vax/4.4 m/s = cos31
    3.8 m/s

    Vay/Va = sin31
    Vay/4.4 m/s = sin31
    2.3 m/s

    Vbx/Vb = cos25
    Vbx = 7.8cos25
    7.1m/s

    Vby/Vb = sin25
    Vby= 7.8sin25
    3.3m/s

    Ay = Vby- Vay / t
    3.3-2.3/ 8.5 s
    0.12 m/s^2

    Ax = Vbx- Vax / t
    7.1 m/s - 3.8 m/s / 8.5 s
    0.4 m/s^2

    a^2 = Ax^2 + Ay^2
    0.16 + 0.0144
    0.174 m/s^2 and then you square root it 0.41 m/s^2

    tantheta = Ay/Ax
    0.12 m/s^2/0.4 m/s^2
    0.3 = 17 degrees

    3. The attempt at a solution

    The bird's avg acceleration is 0.41 m/s^2 [17 degrees N of E]

    I just need to make sure if I did this right, if anyone would clarify this that would be great!!
    thanks
     
  2. jcsd
  3. Mar 4, 2009 #2

    Redbelly98

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    Re: Physics question, solved but need clarification!!

    Welcome to PF :smile:

    It's mostly correct. You'll want to recheck +/- signs for the velocities. Is Northward or Southward the "positive y" direction?
     
  4. Mar 4, 2009 #3

    RS7

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    Re: Physics question, solved but need clarification!!

    oo then if I messed up on the signs I guess my answer is wrong, and northward is the positive y direction I think
     
  5. Mar 4, 2009 #4

    RS7

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    Re: Physics question, solved but need clarification!!

    Vax/Va = cos31
    Vax/4.4 m/s = cos31
    3.8 m/s

    Vay/Va = sin31
    Vay/4.4 m/s = sin31
    - 2.3 m/s

    Vbx/Vb = cos25
    Vbx = 7.8cos25
    7.1m/s

    Vby/Vb = sin25
    Vby= 7.8sin25
    3.3m/s

    Ay = Vby- Vay / t
    3.3 + 2.3/ 8.5 s
    0.7 m/s^2

    Ax = Vbx- Vax / t
    7.1 m/s - 3.8 m/s / 8.5 s
    0.4 m/s^2

    a^2 = Ax^2 + Ay^2
    0.16 + 0.49
    0.65 m/s^2 and then you square root it 0.8 m/s^2

    tantheta = Ay/Ax
    0.7m/s^2/0.4 m/s^2
    1.75 = 60 degrees

    the bird's avg acceleration is 0.8 m/s^2 [60 degrees N of E]

    is this right? :S
    I used the signs for the velocities but not quite sure if I did it right...
     
  6. Mar 4, 2009 #5

    Redbelly98

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    Re: Physics question, solved but need clarification!!

    Looks good. :smile:
     
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