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Unformatted text preview: CONSERVATION OF ENERGY 'CtivPhysiCS can help with these Problems: ji.u Activities in Section 5, Work and Energy 0$ y::;: e, followed by dr=idx for y = i and 0$ x:$ and (b) dr=idx+jdy=(i+j)dy, for 0 :$ y :$ e (since x = y along this path). The work done by gravity (Equation 7-11) is e, wJa} Determine the work done by the frictional force in < moving a block of mass m from point 1 to point 2 .... the two paths shown in Fig. 8-26. The over ...........coefficient friction has the constant value p, over of the surface. (The diagram lies in a horizontal ......plane.) = / F 9 dr = -mg = 1; l 1 i. (-mgj). j dy + 1 l (-mgj). i dx i dy +0= -mge, and ? . WJb) = ( -mgj) (i+ j)dy = -mg dy = -mgt. ~ ~ . r l i..... I I / r (a) I' r---I I I I ' .--- I 2 .. " Of course, these must be the same because gravity is a conservative force. " .- " "...(b) / " .' Problem 3. The force in Fig. 8~22a is given by F = Foj, where Fo is a'constant. The force in Fig. 8-22bis given by F= Fo(x/a)j, where the origin is taken at the lower left corner of the box, a is the width of the square box, and the distance x increases horizontally to the right....
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