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Homework Help: How to draw the angles to find force

  1. Mar 17, 2008 #1
    1. The problem statement, all variables and given/known data

    2. Relevant equations

    I have the picture and everything but i just need help with the angles. Like i am a bit confused about how to draw the angles and stuff please help.
    3. The attempt at a solution
  2. jcsd
  3. Mar 17, 2008 #2
    Use a coordinate plane so that the incline of your ramp, Ff, Ff and Fa are along the x-axis, and Fn is along the y-axis. Then you can figure out the components of the weight using the angle they give you (break the weight into its components along the incline and perpendicular to the incline).
  4. Mar 17, 2008 #3
    so then would this picturehttp://img136.imageshack.us/my.php?image=toottup2.png be correct??
    and to find the x component of the Fg i would have to do (cos30)mg and to find the y component i would have to do (sin30)mg?
  5. Mar 17, 2008 #4
    Sin is opp/hyp and cos is adj/hyp, so you may want to re-check what the y and x-components are for Fg.
  6. Mar 17, 2008 #5
    oo.. yea i messed it up so basically force normal(upward) would be (cos30)mg and force downward would be (sin30)mg? right?
    also would force normal be the same as force gravity?
    Last edited: Mar 17, 2008
  7. Mar 17, 2008 #6
    Downward and upward? Wouldn't that be the same vector?
  8. Mar 17, 2008 #7
    force normal(Fn) is the force that was opposing gravity and force downward is the one labeled Fd so i dnt think they are the same vectors
  9. Mar 17, 2008 #8
    Ah, yes I see what you mean. A problem with your diagram is that there is no applied force, the block is sliding down the ramp due to the force of the x-component of its weight.
  10. Mar 17, 2008 #9
    i think i kind of understand it but i have a quick question. would the y component of Fg always be the same as the Fn?
  11. Mar 17, 2008 #10
    They are the only two forces in the y-direction of your coordinate plane and they are opposing each other.
  12. Mar 17, 2008 #11
    right so would they have the same magnitude?
  13. Mar 17, 2008 #12
    I don't see any other force in the y-direction.
  14. Mar 17, 2008 #13

    ok now do you see the 2 blue forces?? the one pointing down is the y component of the Fg and the one pointing up is Fn. i am just asking if both of those blue vectors would have the same magnitude?
  15. Mar 17, 2008 #14
    Well, if those two forces are the only forces in the y-direction and they're opposing each other, do you think that they are equal?
  16. Mar 17, 2008 #15
    yea because the block stays down it doesnt like go through the incline of go above in the air like it stays on the incline so both the forces have to be the same.
    i m sryy its just my teacher doesnt teach anything he talks about his life so its basically a self study class and i want to understand the material because I know i am going to have to take a year of physics in college and i dont want to go in their knowing nothing. i want to atleast have a background layed.
  17. Mar 17, 2008 #16
    Good, now that you understand why they are equal you can move on.
  18. Mar 17, 2008 #17
    thx a lot! u saved me! lolzz
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