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Homework Help: Need help finding degrees to the right of the forward direct

  1. Oct 13, 2015 #1
    1. The problem statement, all variables and given/known data

    Two forces are applied to a car in an effort to move it, as shown in the figure below. (Let
    F1 = 430 N (10 degrees)
    F2 = 356 N. (30 degrees)
    Assume up and to the right are in the positive directions.)
    (a) What is the resultant vector of these two forces?
    ° to the right of the forward direction=?
    (b)If the car has a mass of 3,000 kg, what acceleration does it have? Ignore friction.
    2. Relevant equations
    (430sin(10)) + 356sin(30)=252.67x
    (430cos(10)) + 356cos(30)=731.78y

    angle = tan-1((731.78y)/(252.67x)) ??

    3. The attempt at a solution
    For part a I got 774.17N for the magnitude and it was correct
    For part b I got 0.244 for the acceleration and it was correct
    But I can not for the life of me solve for angle to the right of the forward direction

    Attached Files:

  2. jcsd
  3. Oct 13, 2015 #2


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    Staff Emeritus
    Science Advisor
    Homework Helper

    This calculation is incorrect. If you look at the diagram, the x-components of each force act in opposite directions, so you can't simply add them together to find the resultant force in the x-direction.

    Always indicate units with your calculations.

    These calculations are OK.

    If you are still having trouble, make a small sketch of the resultant force vector and F1 and F2. You should be able to find the correct angle once you have calculated the correct x-component of the resultant force.
  4. Oct 13, 2015 #3
    When I recalculated my x-component of the resultant force I got 103.33 N and an angle of 81.96 degrees.
    F2x-F1x= Resultant x-component
    (356 N sin(30)) - (430 N sin(10))= 103.33 N
    tan-1=((731.78)/(103.33)) = 81.96
    would 81.96 be the degrees to the right of the forward direction then that the question is asking for?
    Thanks for the clarification and help!
  5. Oct 13, 2015 #4


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    Staff Emeritus
    Science Advisor
    Homework Helper

    Did you draw the resultant and F1 and F2 to see if this calculation is correct?

    I think you have calculated the wrong angle.

    Does it seem reasonable that the resultant of F1 and F2 would act at almost a right angle to them?
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