[填空题]
At each corner of a square r3;ijwy l7o:yaw.vt s-s +ar 5of side l there are rcurj1.9wu02t t4*-a :ydry2hjmq nc point charges of magnitude Q, 2Q, 3Q, and 4Q (Fig. 16–52). Determine the force on (a2 2-jj0*nmwqtuh: yrtcra. dy9cu41 r) the charge 2Q, and (b) the charge 3Q, due to the other three charges.
$F_{2Q}$ = $\frac{kQ^2}{l^2}$
$\theta_{2Q}$ = $^{\circ}$
$F_{3Q}$ = $\frac{kQ^2}{l^2}$
$\theta_{3Q}$ = $^{\circ}$
