# Chapter 25 - Electric Charges and Forces - Exercises and Problems - Page 745: 18

The electric force on Object A is $4.5\times 10^{-3}~N$ in the positive y-direction. The electric force on Object B is $4.5\times 10^{-3}~N$ in the negative y-direction.

#### Work Step by Step

We can find the magnitude of the electric force on each object: $F = \frac{k~q_A~q_B}{r^2}$ $F = \frac{(9.0\times 10^9~N~m^2/C^2)(10\times 10^{-9}~C)(20\times 10^{-9}~C)}{(0.020~m)^2}$ $F = 4.5\times 10^{-3}~N$ Since one charge is positive and one charge is negative, the two charges attract each other. The electric force on Object A is $4.5\times 10^{-3}~N$ in the positive y-direction. The electric force on Object B is $4.5\times 10^{-3}~N$ in the negative y-direction.

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