18. (a) For the net force to be in the +xdirection, the ycomponents of the individual forces must cancel. The angle of the force exerted by the q1= 40 µC charge on 320qC=is 45°, and the angle of force exerted on q3by Qis at –θwhere 12.0 cmtan33.7 .3.0 cm−⎛⎞==°⎜⎟⎝⎠Therefore, cancellation of ycomponents requires ()( )13322||sin 45sin0.02 2 m(0.030 m)(0.020 m)qqQ qkk°=+from which we obtain |Q| = 83 C. Charge Qis “pulling” on
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