1. Advanced Coulomb Problems
Example Enrichment Problems

2. Objects A, B, C, and D are all charged
Objects A, B, C, and D are all charged. A attracts B and repels C, C attracts D, and D has a negative charge. What is the charge on B?
Answer: A is the opposite charge of B A = – (B) A is the same charge as C A = C C is the opposite charge of D C = – (D) D is negative. D = – Therefore, C = A = – (B) – (D) = A = – (B) – (D) = – (B) D = B B = –

3. Three equally charged objects A, B, and C are placed left to right in a straight line. A is located 8.0 cm to the left of B and C is 2.0 cm to the right of B. The force of B on C is +5.0 x 10-5 N. a. What is the force of A on B? b. What is the net force on B?
Answer: First draw and label the information given
All objects are equally charged so qA = qB = qC and Force of B on C can be written as FBC = +5.0 x 10-5 N.
where “rBC” is the distance from B to C so later “rBA” is the distance from B to A.
Since qB = qC , just call the charges qB and qC “q” and solve for “q”

4. Three equally charged objects A, B, and C are placed left to right in a straight line. A is located 8.0 cm to the left of B and C is 2.0 cm to the right of B. The force of B on C is +5.0 x 10-5 N. a. What is the force of A on B? b. What is the net force on B?
Answer: First draw and label the information given
All objects are equally charged so qA = qB = qC and Force of B on C can be written as FBC = +5.0 x 10-5 N.
and

5. Three equally charged objects A, B, and C are placed left to right in a straight line. A is located 8.0 cm to the left of B and C is 2.0 cm to the right of B. The force of B on C is +5.0 x 10-5 N. a. What is the force of A on B? b. What is the net force on B?
Answer: First draw and label the information given
All objects are equally charged so qA = qB = qC and Force of B on C can be written as FBC = +5.0 x 10-5 N.
and
A Free-Body Diagram of the forces on “B” is needed to get the net force on “B”.
A Free-Body Diagram of the forces on “B”
Like Charges Repel
FAB
FBC
FBA
FCB

6. Charges 1.0 mC, 4.0 mC, and 9.0 mC are placed at three corners of a square on a side as shown. What is the net force on the 4.0 mC charge?