r = (4002 + 3002)1/2 = 500 nm

= tan-1 400/300 = 53.1½
 

EA = kQA/r2 and EB = kQB/r2 = 3kQA/r2
 

x comp:

Eax + Ebx = (kQA/r2)cos q - (3kQA/r2)cosq = -(2kQA/r2)cosq = 2(kQA/r2)(3/5)

= (6/5)(9X109)(5X10-6)/600X10-9 = 0.15 N/C
 

y comp:

Eay + Eby = (kQA/r2)sinq + (3kQA/r2)sinq = (4kQA/r2)sinq = 4(kQA/r2)(4/5)

= (16/5)(9X109)(5X10-6)/600X10-9 = 0.40 N/C
 

E = (0.152 + 0.402)1/2 = 0.43 N/C

at an angle f where

f = tan-10.4/0.15 = 69½ up to the left.
 

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