U4_wksh3_ForceDiagrams_06 - COMPILATION Unit 4 worksheet 3...

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COMPILATION: Unit 4 -- worksheet 3, problem 5: force diagrams for inclined planes COMPILATION: Unit 4 -- worksheet 3, problem 5: force diagrams for inclined planes Date:    Wed, 15 Feb 2006  From:   Andrew Schuetze  Subject: Unit 4 wksht 3 prob. 5 Problem 5 has a block on a frictionless ramp with a 30 degree slope held in place by a tension  force.  The block is 20 Kg. Find the normal and tension force. Is this a case where one needs to rotate the coordinate system by 30 degrees to solve? Without rotating I get the following equations:      Sum of all Forces in X  = (-) FTx  +  FNx  = 0      Sum of all Forces in Y  = (-) FG  + FTy  +  FNy  = 0 With only F of G and no symmetry I was stuck. Rotating the coordinate system by 30 degrees I get the following:      Sum of all Forces in the X = (-) FT + FGx  = 0      Sum of all Forces in the Y = (-) FGy + FN  = 0 ------------------------------- Date:    Thu, 16 Feb 2006  From:    "K. Fincher"       Thanks to the modeling workshops, I can answer your question with confidence!   I keep the  horizontal axis parallel to the surface the object is on.   This makes the weight of the box straight  down, as usual, but not along any axes.  Break the weight into its horizontal and vertical  components and then the problem can easily be solved. ------------------------------ Date:    Thu, 16 Feb 2006  From:    "Cline, Brad"       It is best to  rotate the coordinate system by 30 degrees as you did in your second scenario.    This makes the whole problem more manageable to the students and (as you showed) simplifies  the problem down to two forces in the x and two in the y directions with both giving a net force of zero.  I usually approach all incline problems with this approach by explaining that the weight  of the object is no longer in line with the x-y coordinate system but instead lies between the two  axes which have been tilted by the angle of the incline.  Thus you solve for the Fx and Fy  components of the weight.  It still takes time for the students to"get" this, but I've found this  approach to the problem to be much more understandable.  ------------------------------ Date:    Thu, 16 Feb 2006  From:    "Pifer, Rebecca"  It's a lot easier if you do rotate the coordinate system.  If you don't want to, you can also use 
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