PLEASE PROVIDE REASONING: SIMILAR QUESTION ON HERE HAD THREE DIFFERENT ANSWERS P

Question

PLEASE PROVIDE REASONING: SIMILAR QUESTION ON HERE HAD THREE DIFFERENT ANSWERS POSTED

Two positive charges, one of magntude Q and the other of magnitude 2Q, and one negative charge of magnitude -Q are placed on a straight line. The -Q charge is in the middle with Q to its left and 2Q to its right. The distance between the charge on the left and the charge in the middle is d, while that between the charge in the middle and the charge on the right is 2d.

A) Find both the magnitude and direction of the net force on the positive charge on the left.

B) Find both the magnitude and direction of the net force on the negative charge in the middle.

Explanation / Answer

Given

charges Q,-Q,2Q

   Q ------ -Q ----------------2Q

   <----d----><-------2d-------->

1) the force on q due to -Q,2Q is ?

from Coulomb's law F = kq1q2/r^2

       F = k(Q*(Q)/d^2 - Q*2Q/9d^2)

       F = kQ^2/d^2(1-2/9)

       F = (kQ^2/d^2)(7/9)

the direction is along + x direction

2)net force on -ve charge is

   due to Q is in the -ve x direction F = - k(Q*(Q)/d^2

and due to charge 2Q is along +ve x direction F = kQ*2Q /4d^2

       net force F =kQ^2/d^2(0.5-1)

           F = -0.5 kQ^2/d^2

so the direction is along the -ve x direction

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