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Unformatted text preview: Phy 9A-C, Midterm 2 Solutions, Page 1 of 2 5/20/11 Yellow F T F N mg f F N mg f Phyiscs 9A-C Midterm 2 Solutions Cole Yellow a)F=0b)never,c)both,d)position,e)equalto,f)spinfaster,g) K m >K M , h)none,i)0,j)momentum. a)(10pts) Usetheworkenergytheorem W T =K. W F T = F T x = 500N ( ) 5m ( ) = 2500J While F N doesnoworkitisneededforthe frictionforce: F y =F N -mg cos36.9=0 F N = mg cos36.9 = 4 5 mg W f = k F N x = k 4 5 mg x W f = 0.35 ( ) 4 5 30kg ( ) 9.8m/s 2 ( ) 5m ( ) = 411.6J . Theonlyotherforcedoingworkisgravity: W g = mg h = 30kg ( ) 9.8m/s 2 ( ) 3m ( ) = 882.0J882....
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