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Physics problems with Newton's Law

  1. Sep 21, 2004 #1
    These problems are really giving me fits, I would really appreciate some help.

    A 12200 kg sailboat experiences an eastward
    force of 27400 N due to tide pushing its hull
    while the wind pushes the sails with a force of
    56200 N directed toward the northwest (45±
    westward of North or 45± northward ofWest).
    What is the magnitude of the resultant ac-
    celeration of the sailboat?

    I'm using Fr= square root of (Frx squared)+(Fry squared) but I'm still not getting it right. I'm thinking that maybe I drew the free body diagram wrong. Any help?

    Now for this one

    The distance between two telephone poles is
    32 m. When a 1:15 kg bird lands on the
    telephone wire midway between the poles, the
    wire sags 0:182 m.
    The acceleration of gravity is 9:8 m=s2 :
    How much tension in the wire does the
    bird produce? Ignore the weight of the wire.

    So far I've drawn the diagram and got a hypotenuse of 16.001 m, but I'm unsure how to finish the problem.

    Any help would be much appreciated.
  2. jcsd
  3. Sep 22, 2004 #2
    1. Find the magnitude using the cosine law.
    2. use F=ma to find the magnitude of a.
    It is easier to use the unit vector i and j. but i am afraid you haven't learnt that yet. so we will approach it geometrically.

    Attached Files:

  4. Sep 22, 2004 #3
    First problem (sail boat)

    check the attachment

    Fx = F(east) - F(northwest)Xcos45 = -12339 N
    Fy = F(northwest)Xsin45 = 39739 N
    Fnet = Squareroot of (Fx^2 + Fy^2)
    then, Fnet = ma
    a = Fnet/mass = 3.4 m/s

    Attached Files:

  5. Sep 22, 2004 #4
    2nd problem

    ok the hyp that you got is good.
    a^2 + b^2 = c^2
    a= 16
    b = .182
    c = 16.001 using the formula. Good you got until this point.

    2nd step= get the angle theta. (see diagram)

    90-tan (16/.182) = theta

    step 3 = Get the tension by adding the Forces on the y axes. See diagram

    Attached Files:

  6. Sep 22, 2004 #5
    Free body diagram : Attached file.

    Attached Files:

  7. Sep 22, 2004 #6
    of course, I didn't draw the other tension on the other side because is understood.
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