Math Problem Statement

Two point charges are placed over the x-axis as follows: charge q1=+3nC is at x=0.26m, and charge q2=+6nC is at x=-0.45m. Find the magnitude and direction of the total force exerted by these two charges over a negative point charge q3=-8nC that is at x=0m.

Solution

To solve this problem, we will use Coulomb's Law to calculate the force between each pair of charges, and then we will determine the total force exerted on q3q_3 by q1q_1 and q2q_2.

Step 1: Coulomb's Law

The force between two point charges is given by Coulomb's Law:

F=keq1q2r2F = k_e \frac{|q_1 q_2|}{r^2}

where:

  • FF is the magnitude of the force between the charges,
  • ke=8.99×109Nm2/C2k_e = 8.99 \times 10^9 \, \text{N}\cdot\text{m}^2/\text{C}^2 is Coulomb's constant,
  • q1q_1 and q2q_2 are the magnitudes of the charges,
  • rr is the distance between the charges.

Step 2: Force on q3q_3 due to q1q_1

Charge q1=+3nC=3×109Cq_1 = +3 \, \text{nC} = 3 \times 10^{-9} \, \text{C} is located at x=0.26mx = 0.26 \, \text{m}, and charge q3=8nC=8×109Cq_3 = -8 \, \text{nC} = -8 \times 10^{-9} \, \text{C} is located at x=0mx = 0 \, \text{m}. The distance between q1q_1 and q3q_3 is:

r13=0.260=0.26mr_{13} = |0.26 - 0| = 0.26 \, \text{m}

The magnitude of the force between q1q_1 and q3q_3 is:

F13=keq1q3r132=(8.99×109)3×109×(8×109)(0.26)2F_{13} = k_e \frac{|q_1 q_3|}{r_{13}^2} = (8.99 \times 10^9) \frac{|3 \times 10^{-9} \times (-8 \times 10^{-9})|}{(0.26)^2}

Step 3: Force on q3q_3 due to q2q_2

Charge q2=+6nC=6×109Cq_2 = +6 \, \text{nC} = 6 \times 10^{-9} \, \text{C} is located at x=0.45mx = -0.45 \, \text{m}. The distance between q2q_2 and q3q_3 is:

r23=0(0.45)=0.45mr_{23} = |0 - (-0.45)| = 0.45 \, \text{m}

The magnitude of the force between q2q_2 and q3q_3 is:

F23=keq2q3r232=(8.99×109)6×109×(8×109)(0.45)2F_{23} = k_e \frac{|q_2 q_3|}{r_{23}^2} = (8.99 \times 10^9) \frac{|6 \times 10^{-9} \times (-8 \times 10^{-9})|}{(0.45)^2}

Step 4: Direction of Forces

  • The force between q1q_1 and q3q_3 is attractive (since q1q_1 is positive and q3q_3 is negative), so the force will be directed towards q1q_1, i.e., in the positive x-direction.
  • The force between q2q_2 and q3q_3 is also attractive (since q2q_2 is positive and q3q_3 is negative), so the force will be directed towards q2q_2, i.e., in the negative x-direction.

Step 5: Total Force on q3q_3

To find the total force, we sum the forces considering their directions:

  • F13F_{13} is positive (towards q1q_1),
  • F23F_{23} is negative (towards q2q_2).

The total force is:

Ftotal=F13F23F_{\text{total}} = F_{13} - F_{23}

Let me compute these values.The forces between the charges are as follows:

  • The magnitude of the force between q1q_1 and q3q_3 is F13=3.19×106NF_{13} = 3.19 \times 10^{-6} \, \text{N} in the positive x-direction.
  • The magnitude of the force between q2q_2 and q3q_3 is F23=2.13×106NF_{23} = 2.13 \times 10^{-6} \, \text{N} in the negative x-direction.

Thus, the total force exerted on q3q_3 is:

Ftotal=1.06×106NF_{\text{total}} = 1.06 \times 10^{-6} \, \text{N}

This force is directed towards q1q_1 (in the positive x-direction), as F13F_{13} is larger than F23F_{23}.

Would you like a deeper explanation or more details?

Here are some related questions:

  1. What happens if q1q_1 and q2q_2 have opposite charges?
  2. How does the force change if we move q3q_3 closer to q1q_1?
  3. What if q3q_3 were placed exactly between q1q_1 and q2q_2?
  4. How would the force change if q3q_3 had a different magnitude?
  5. What if the distances between the charges were doubled?

Tip: Remember, forces between charges decrease with the square of the distance between them.

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Math Problem Analysis

Mathematical Concepts

Electrostatics
Coulomb's Law
Vector addition of forces

Formulas

Coulomb's Law: F = k_e * |q1 * q2| / r^2
Total Force: F_total = F_13 - F_23

Theorems

Coulomb's Law

Suitable Grade Level

Grades 10-12 (Advanced Physics)