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Accelerometer question

  1. Mar 5, 2016 #1
    1. The problem statement, all variables and given/known data
    A small mass m hangs from a thin string and can swing like a pendulum. You attach it above the window of your car. When the car is at rest, the string hands vertically. What angle θ does the string make when the car accelerates at a constant a=1.20m/s^2?

    2. Relevant equations
    I assume a relevant equation is ƩF = ma

    3. The attempt at a solution
    This is already solved in my book but I was trying to do it by myself

    I know I need to find ƩF = may and ƩF = max

    And I know that ƩF = may is FTcosθ -mg=may

    And that ƩF = max is FTsinθ =max

    My book says that FTcosθ -mg =0, and my question is why???? is ay=0? How can I know that?
     
  2. jcsd
  3. Mar 5, 2016 #2

    Doc Al

    User Avatar

    Staff: Mentor

    Presumably the car is accelerating horizontally, not vertically.
     
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