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Unformatted text preview: ergy is llU =':lU33  Ul U33 0 mgtly = (55x9.8 N)(32x3.5 mj:;;; 6004 kJ. (b) At the fiftyninth floor, U59  Ul (55x9.8 N)x (58 x 3.5 m) = 109 kJ. (c) Street level is th'e zero of "1 potentia! energy, UI == O. Note that the differences in potential energy between any two levels ai!e the same as in Example 81, e.g., U59  U33 == (109160.4) kJ 49.0 kJ. = = = = 7. Show using Equation 82bthatthe potential energy difference between the ground and a distance h above the ground is mgh regardless of whether you choose the yaxis upward or downward. Solution
Equation 82b gives the potential energy difference for a constant force in the y direction, AU U(Y2)  U(Yl) = FY(Y2  yd. If you take the yaxis upward, with the ground at YI, the gravitational force is Fy = mg, while a point a distance h above ground is Y2 h+ YI' Then AU = (mg)h = mgh. On the other hand, if the yaxis is downward, then Fy = mg but Y2 = h + yl, so AU = (mg)(h) mgh is the = = Problem ;
.1 5. Find the potential energy of a 70kg hi~...
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This note was uploaded on 07/27/2009 for the course PHYSICS 101 taught by Professor Wormer during the Spring '08 term at NYU Poly.
 Spring '08
 WORMER
 Physics, Conservation Of Energy, Energy, Work

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