You're mostly correct, except for the assumption that C would be the variable that changes. C will stay constant, and relative permittivity will go up accordingly.
Homework Statement
Two boxes, A & B are on a flat surface, and are connected by a massless string at an angle of 7° to the horizontal. Box A masses 9kg, box b 4kg. The boxes are pulled by a string connected to box A at an angle of 23° to the horizontal. Find the force required in order to...