Final answer:
Once yf is provided, the potential difference can be calculated using the appropriate electrostatic formula.
Step-by-step explanation:
The question seems to be asking for the potential difference in an electrical context, requiring knowledge of electric potentials and fields. When dealing with potential difference in physics, especially within the context of electrostatics, we're often talking about the work done per unit charge in moving a charge between two points in a field set up by other charges.
From the information and various examples provided, it can be seen that potential difference is the key concept here. It is usually calculated in volts (V) and can be determined using the formula:
V = k * Q * (1/ri - 1/rf),
where V is the potential difference, Q is the charge that creates the field, ri is the initial distance from the charge, rf is the final distance from the charge, and k is Coulomb's constant.
Unfortunately, the final position yf is not given in the original question. However, if yf were known, we could apply this formula, substituting the distances into the places of ri and rf accordingly, to find the potential difference between the two points in the electric field.