Determine the change in electric potential energy of a system of two charged obj

Question

Determine the change in electric potential energy of a system of two charged objects when a -1.2  mC charged object and a -5.2 mC charged object move from an initial separation of 470 cm to a final separation of 190 cm .

A.
If the potential energy is zero at infinity, what is the potential energy of the initial state?
Express your answer to two significant figures and include the appropriate units.

B.

If the potential energy is zero at infinity, what is the potential energy of the final state?
Express your answer to two significant figures and include the appropriate units.

C.

What is the change in potential energy between the initial state when the separation is 470 cm to a final state when the separation is 190 cm ?
Express your answer to two significant figures and include the appropriate units.

Explanation / Answer

A.

U= kq1q2 / r1=9*10^9*-1.2*10^-3*-5.2*10^-3/4.70

U=1.2*10^4 J

B.

U= kq1q2 / r2=9*10^9*-1.2*10^-3*-5.2*10^-3/1.90

U=3.0*10^4 J

C.

Change in potential energy

U= kq1q2[1/r2 - 1/r1]=9*10^9*-1.2*10^-3*-5.2*10^-3*[1/1.90 - 1/4.70]

U=1.8*10^4 J

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