Question

Pictured above is a red point charge and a blue point charge.
The blue point charge is moved from loication 1 to location 2. The force between the point charges is 5.00 N when blue charge is at location 1.
How much force exist between the point charges when the blue charges is at location 2?

• A. 25.0 N
• B. 30.0 N
• C. 125 N
• D. 180 N
• E. 1.0 N

Answer 1

The correct option is D 180 N

When the blue charges is at location 1, the force between the charges, $F=\frac{k{q}_1{q}_2}{r^2}$

or $5=\frac{k{q}_1{q}_2}{(d+5d{)}^2}=\frac{k{q}_1{q}_2}{36d^2}....\left(1\right)$

When the blue charges is at location 2, the force between the charges,

$F^{\prime }=\frac{k{q}_1{q}_2}{d^2}....\left(2\right)$

using (1), (2), $F^{\prime }=5\times 36=180N$