Final answer:
The electric potential at a point midway between two charges is found by calculating the potential due to each charge separately and summing them, as electric potential is a scalar quantity. The midpoint distance is half the separation between the charges.
Step-by-step explanation:
To find the electric potential at a point midway between the two charges Q1 and Q2, we need to use the formula for the electric potential due to a point charge V = kQ/r, where V is the electric potential, k is Coulomb's constant (8.99 × 109 Nm2/C2), Q is the charge, and r is the distance from the charge to the point of interest.
At the midpoint, the distances to both charges are equal, so we can calculate each potential separately and then sum them because electric potential is a scalar quantity. The potential due to Q1 is V1 = kQ1/r and the potential due to Q2 is V2 = kQ2/r. Since one charge is positive and the other negative, their potentials will add algebraically to give the total potential at the midpoint.
Applying the values, for Q1 = +5.10 nC and Q2 = -1.40 nC separated by 25.0 cm (0.25 m), and r being half of that distance (0.125 m), the total potential V = V1 + V2 = (k*5.10*10-9C/0.125 m) + (k*(-1.40*10-9C)/0.125 m).
Calculating each term and summing them will yield the final answer.