Key to problems 2009-new

Key to problems 2009-new - 23 To convert to ergs the number...

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Key to first problem on exam/: the amount of work, potential energy, to produce arrangement A is: (1x3)/3 + (3 x-5)/3 +(1 x-5)/3. The amount of work to produce B is: (1 x 3)/3 + (3 x -5)/4.2 +(1 X-5)/3. The amount of work to go from a to b is equal the work to make B minus the work to make A. In the units used above, the units of work will be ergs. Key to second problem on exam: When the two boxes are separated more surface is exposed to water. The increased surface is (50 X 20) x 2 A 2 . The amount of work required to increase the surface is the previous number times 70 cals/A 2 /mole. This is the amount of work if one mole of box is used. Since we are interested in one molecule the above number is divided by the number of molecules in one mole, which is 6 x 10
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Unformatted text preview: 23 . To convert to ergs the number is multiplied by the number of joules in a cal, 4.18, and the number of ergs in a joule, 10 7 . Key to energy problem: Energy is conserved, so the sum of the kinetic energy plus the potential energy is constant. Since there is no velocity of any particle in A the kinetic energy is zero. The amount of potential energy is (5 x6)/3 + (6 x 7)/4 +(7 x 5)/3. The total energy of B must equal this number because of conservation of energy. The potential energy of B is: (5 x 7)/10 + (7 x 6)/15 + (5 x 6)/20. Since energy of A = energy of B, The potential energy of A minus the potential energy of B = the kinetic energy of B, that is potential energy(A) + kinetic energy of A = potential energy of B + kinetic energy of B....
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