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Homework Help: Uniform Circular motion

  1. Oct 13, 2011 #1
    1. The problem statement, all variables and given/known data

    A toy airplane is tied to the ceiling with a string. When the airplane's motor is started, it moves with a constant speed of 1.01 m/s in a horizontal circle, as illustrated in the figure. If the angle the string makes with the vertical is 38°, and the tension of the string is 1.1N:

    (a) Find the radius of the horizontal circle of the plane
    b) Find the mass of the plane.

    3. The attempt at a solution

    Im having problems understanding how to attack physics problems a point in the right direction would help! I think Im supposed to split this into components using the angle. I drew a FBD with only tension and mg as acting forces. Do I use Newtons 2nd law?
  2. jcsd
  3. Oct 14, 2011 #2
    The first thing to do is to make a picture. You'll notice that there are only 2 forces acting on the plane. Namely, tension and gravity.

    You know that the horizontal motion is circular, so that leads to Fnet = mv^2/r
    You know Fnet in the x direction, and velocity. Find a relationship to solve for the mass and then you'll only be left with radius as a variable, which is easily solved for.
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