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Thread: Simple vectors problem

  1. #1
    Junior Member
    Nov 2014

    Simple vectors problem

    This is my third time learning about vectors this year (The first being in Calc III, the second time being in linear algebra, and the third being in Physics)

    And you won't believe I'm still unsure.

    The question is:

    Vector A has y-component A = 17.0m. A makes an angle of 40.0 degrees counterclockwise from the positive y axis. What is the x component of A?

    I did some work and I got the x component to be 14.26 meters.

    I set my vector A to have components: A = <Acos(50 degrees), Asin(50 degrees)>, then later I got A to be 17/sin(50 degrees) by letting Asin(50 degrees) to be 17.
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  2. #2
    MHF Contributor
    Oct 2009

    Re: Simple vectors problem

    Draw a diagram. The vector (from the origin) lies in the 2nd quadrant. You should be using 130 degrees as the angle not 50. This will give you -14.26m for the x-component.

    If you are going to use the "formula" (A cos (theta), A sin (theta)), then the angle must be measured counter-clockwise from the positive x-axis.

    My advice would be to forget the "formula" for now. Draw a diagram of the vector (starting at the origin) on a set of axes. Use simple right-angled triangle trig to find what you need, and attach neg signs as needed.
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