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Two point charges are stationary and separated by a distance [tex]R[/tex]. Which one of the following pairs of charges results in the largest repulsive force?

Equation: [tex]F = \frac{k q_1 q_2}{R^2}[/tex]

A. [tex]-3q[/tex] and [tex]-2q[/tex]

B. [tex]+3q[/tex] and [tex]-2q[/tex]

C. [tex]-2q[/tex] and [tex]+4q[/tex]


Sagot :

To determine which pair of charges result in the largest repulsive force, we'll utilize the Coulomb's Law equation:
[tex]\[ F = \frac{k \cdot q_1 \cdot q_2}{R^2} \][/tex]

Where:
- [tex]\( F \)[/tex] is the force between two charges,
- [tex]\( k \)[/tex] is Coulomb's constant,
- [tex]\( q_1 \)[/tex] and [tex]\( q_2 \)[/tex] are the magnitudes of the two charges,
- [tex]\( R \)[/tex] is the distance between the charges.

Given pairs of charges are:
1. [tex]\(-3q\)[/tex] and [tex]\(-2q\)[/tex]
2. [tex]\(+3q\)[/tex] and [tex]\(-2q\)[/tex]
3. [tex]\(-2q\)[/tex] and [tex]\(+4q\)[/tex]

We should calculate the force for each given pair to determine which one has the largest repulsive force.

### Step-by-step Calculation:

#### Pair 1: [tex]\(-3q\)[/tex] and [tex]\(-2q\)[/tex]
[tex]\[ F_1 = \frac{k \cdot (-3q) \cdot (-2q)}{R^2} = \frac{k \cdot 6q^2}{R^2} \][/tex]
Since both charges are negative, the product [tex]\((-3q) \cdot (-2q)\)[/tex] is positive, leading to a repulsive force.

#### Pair 2: [tex]\(+3q\)[/tex] and [tex]\(-2q\)[/tex]
[tex]\[ F_2 = \frac{k \cdot (+3q) \cdot (-2q)}{R^2} = \frac{k \cdot (-6q^2)}{R^2} \][/tex]
The product [tex]\((+3q) \cdot (-2q)\)[/tex] is negative, leading to an attractive force, not repulsive.

#### Pair 3: [tex]\(-2q\)[/tex] and [tex]\(+4q\)[/tex]
[tex]\[ F_3 = \frac{k \cdot (-2q) \cdot (+4q)}{R^2} = \frac{k \cdot (-8q^2)}{R^2} \][/tex]
The product [tex]\((-2q) \cdot (+4q)\)[/tex] is negative, leading to an attractive force, not repulsive.

### Comparing Repulsive Forces:
Only Pair 1 results in a repulsive force. Therefore, the force corresponding to Pair 1 is:
[tex]\[ F_1 = \frac{6kq^2}{R^2} \][/tex]

After following through with the calculations, we see that the:
- Force for Pair 1 is [tex]\( 6.0 \)[/tex] units (repulsive force),
- Forces for Pair 2 and Pair 3 are -6.0 and -8.0 units (attractive forces).

Therefore, the largest repulsive force is produced by the pair of charges:
[tex]\(\boxed{-3q \text{ and } -2q}\)[/tex]