Please help!!! I have a physics exam tomorrow and I just can't wrap my head around this one!

Three charged particles lie on the same straight line. Their charges are equal:

qA=qB=qC=0.5 microcoulombs

Charged particle B is in between particles A and C, in the middle. What is the intensity of the electrostatic force acting on particle A? The distance between A and C is 20 meters. Particles B and C are fixed in place.

Formula for the electrostatic force:
[tex] f = k \times \frac{q1 \times q2}{r {}^{2} } [/tex]
The answer is 28 micronewtons, but I don't understand how they got that solution?

Respuesta :

The total electrostatic force on charge A is [tex]28 \mu N[/tex]

Explanation:

The magnitude of the electrostatic force between two charges is given by Coulomb's law:

[tex]F=k\frac{q_1 q_2}{r^2}[/tex]

where:

[tex]k=8.99\cdot 10^9 Nm^{-2}C^{-2}[/tex] is the Coulomb's constant

[tex]q_1, q_2[/tex] are the two charges

r is the separation between the two charges

Here we have three positively charged particles A,B and C, located at the following positions:

[tex]x_A = 0\\x_B = 10 m\\x_C = 20 m[/tex]

The magnitudes of the three charges are:

[tex]q_A = q_B = q_C = 0.5 \mu C = 0.5\cdot 10^{-6}C[/tex]

The force exerted by B on A is to the left (because the force between two positive charges is repulsive), and the force exerted by C on A is also to the left (also repulsive). Therefore, the net force on A is just the sum of the two forces exerted by charges B and C:

[tex]F_A = F_{BA} + F_{CA} = k\frac{q_B q_A}{(x_B-x_A)^2}+k\frac{q_C q_A}{(x_C-x_A)^2}=\\=(8.99\cdot 10^9) \frac{(0.5\cdot 10^{-6})^2}{(10)^2}+(8.99\cdot 10^9) \frac{(0.5\cdot 10^{-6})^2}{(20)^2}=2.8\cdot 10^{-5} N = 28 \mu N[/tex]

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