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Homework Help: Inclined Plane

  1. Jul 29, 2011 #1
    I'm facing a pretty silly problem and I will appreciate if you can help me.
    I face the following diagram:
    [PLAIN]http://img808.imageshack.us/img808/6273/inclinedplane.jpg [Broken]

    Forget about the all the missing values in the painting(like that cart's mass, the value of θ, etc..) they are irrelevant, my question is about a principle.

    Now, what I need to figure out is the component gravity acting along the ramp.
    To figure it out I created a little triangle, placed the right angles, and marked the force acting along the ramp(which I need to figure out) as H:
    [PLAIN]http://img30.imageshack.us/img30/189/markedinclinedplane.jpg [Broken]

    So, in order to figure out H, I did the following:

    sinθ = mg/H
    H = mg/sinθ

    Pretty easy am I right? Except according to the book I'm reading the right answer is:
    H = mg * sinθ

    How can it be? I didn't draw the triangle right? Is there other way to figure the force acting along the ramp?

    Thank in advanced!
    Last edited by a moderator: May 5, 2017
  2. jcsd
  3. Jul 29, 2011 #2

    Doc Al

    User Avatar

    Staff: Mentor

    You drew the wrong triangle. Since gravity is the force that you're trying to find the components of, it must be the hypotenuse of your right triangle (not one of the other sides, like you have it). The components of a force must always be smaller than the force itself.

    Read this: http://www.physicsclassroom.com/Class/vectors/u3l3e.cfm" [Broken]
    Last edited by a moderator: May 5, 2017
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