AP Physics 2: Algebra-Based Practice Quiz: Electric Potential Energy
Written by AP Content Team, Verified for 2026 AP Exams, Last updated: May 2026
Test your understanding with short quizzes. This quiz has 10 questions to check your progress.
Question 1 of 10
All Questions (10)
A) The work required by an external force to assemble the charges from an infinite separation.
B) The kinetic energy the charges gain as they move from infinity.
C) The force exerted by one charge on the other.
D) The total charge of the system divided by the distance between the charges.
Correct Answer: A
The provided content explicitly states that 'The electric potential energy of a system of two point charges equals the amount of work required for an external force to bring the point charges to their current positions from infinitely far away.'
A) U_new = 2 * U_original
B) U_new = 4 * U_original
C) U_new = (1/2) * U_original
D) U_new = (1/4) * U_original
Correct Answer: C
The formula for electric potential energy is U_E = k * (q1*q2)/r. Since U_E is inversely proportional to the distance r, doubling the distance (r -> 2r) will result in the potential energy being halved (U_E -> U_E/2).
A) U_E is positive, because work must be done by an external force to keep the charges apart.
B) U_E is negative, because the product of the charges (q1*q2) is negative.
C) U_E is zero, because the net charge of the system is zero.
D) U_E is undefined, because the charges are of opposite signs.
Correct Answer: B
Using the formula U_E = k * (q1*q2)/r, if q1 is positive (+q) and q2 is negative (-q), their product (q1*q2) will be negative. This results in a negative electric potential energy for the system.
A) By finding the potential energy between the two charges that are farthest apart.
B) By calculating the average of the potential energies of the three possible pairs of charges.
C) By summing the individual potential energies of the interactions between (q1, q2), (q1, q3), and (q2, q3).
D) By multiplying the potential energies of the three possible pairs of charges.
Correct Answer: C
The provided content states that 'The total electric potential energy of a system can be determined by finding the sum of the electric potential energies of the individual interactions between each pair of charged objects in the system.' For three charges, there are three pairs: (q1, q2), (q1, q3), and (q2, q3).
A) U_E = k * (q1*q2) / r^2
B) U_E = k * (q1+q2) / r
C) U_E = k * q1*q2 * r
D) U_E = k * (q1*q2) / r
Correct Answer: D
The provided content gives the equation for the electric potential energy of two charged objects as U_E = (1/(4πε₀)) * (q1*q2)/r = k * (q1*q2)/r.
A) U / 3
B) U
C) 3U
D) 9U
Correct Answer: B
The original energy is U = k * (q1*q2)/r. The new energy is U_new = k * ((3*q1)*q2)/(3*r). The factors of 3 in the numerator and denominator cancel out, so U_new = k * (q1*q2)/r = U. The potential energy remains unchanged.
A) touching each other (r approaches 0).
B) separated by exactly one meter (r = 1 m).
C) infinitely far apart (r approaches ∞).
D) equal and opposite in sign.
Correct Answer: C
The definition of electric potential energy is the work done to bring charges from infinitely far away. This implies that the reference point, where potential energy is zero, is at infinite separation. Mathematically, in the formula U_E = k * (q1*q2)/r, as r approaches infinity, U_E approaches zero.
A) It decreases, because the new charge shields the original two.
B) It remains the same, as the interaction between q1 and q2 is unchanged.
C) It increases, because new positive potential energy terms are added for the interactions with q3.
D) The change cannot be determined without knowing the exact positions.
Correct Answer: C
The total potential energy is the sum of the energies of all pairs. The initial energy is U_12 = k*(q1*q2)/r_12. When q3 is added, the new total energy is U_total = U_12 + U_13 + U_23. Since all charges are positive, the new terms U_13 and U_23 are positive, thus increasing the total electric potential energy of the system.
A) U_E / 4
B) U_E / 2
C) 2 * U_E
D) 4 * U_E
Correct Answer: D
The electric potential energy is given by U_E = k * (q1*q2)/r. If both charges are doubled, the new energy is U_new = k * ((2*q1)*(2*q2))/r = 4 * k * (q1*q2)/r = 4 * U_E. The energy becomes four times larger.
A) Both charges must be positive.
B) Both charges must be negative.
C) The charges must have opposite signs.
D) The charges must have the same sign (both positive or both negative).
Correct Answer: D
The electric potential energy is equal to the work done by an external force to assemble the charges. If the work done is positive, the potential energy U_E is positive. From the formula U_E = k * (q1*q2)/r, for U_E to be positive, the product q1*q2 must be positive. This occurs only when both charges have the same sign (either both positive or both negative).