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Homework Help: Im Dead

  1. Jun 3, 2007 #1
    :cry: Im riting a fisix exam on Toosday and im officially Screwed!!!

    I cant do vectors and incline planes at all

    im going to die:cry:

    Please help:bugeye:

    Here's probly tha simplest problem in the world... and i can't do it...

    a 20 kg box is released on a 30 degree incline with an acceleration of o.25m/s.
    wots tha force of friction impeding its motion?

    Yes, i am stooopid.
  2. jcsd
  3. Jun 3, 2007 #2

    F(gravity)=mg. Component along plane is mg sin 30. (Component normal to plane is mg cos 30). Remember which way around those are by considering if the angle was 0 (sin 0 = 0, cos 0 = 1).

    F(friction)=uN, where the normal force N must equal the normal component of gravity (otherwise it would move into or off from the surface).

    Combining those, total force along the plane is simply the gravity component minus friction. Also the total force is F=ma.
  4. Jun 3, 2007 #3

    Meir Achuz

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    Science Advisor
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    Gold Member

    Draw a good free body diagram.
    Start with the basics.
  5. Jun 3, 2007 #4
    i reeli, reeli wish dat i cud say..." Thanks, guys, i got it!!" ... but i cant.

    thanks anyway... i'll just have to create sum Awesome crib notes for Toosday. Actually, i got a friend who'd do tha test for me... nd let me rite my name on it.

    Actually... I Got it!!! Yippy!!! Thanks, guys, I got it!!!" lol
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