The answer is Resonance. Think of the bass on a speaker and if you place a glass of water onto a table or flat surface, it will start to vibrate/ shake because of the musics beats bass.
Table salt mixed in water is a conductor. When mixed with water, sodium chloride splits into two different electrically charged ions - Na+ ions and Cl- ions. The water solution will then have two terminals, positive and negative, making it possible for electric current to pass through.
The question is poorly worded, and makes it harder for the student to learn the basics of the subject. "Potential Difference" is the difference in electrical potential between two places in an electric field ... not in electrical potential energy.
Explanation:
Given that, the height of the tide measured at a seaside community varies according to the number of hours t after midnight. The height is given by the equation as :

When the tide first be at 6 ft, put h = 6 ft in above equation as :


On solving the above equation to find the value of t. It is equal to :
t = 3.551 seconds
or
t = 8.449 seconds
So, the tide of 6 ft is at 3.551 seconds and 8.449 seconds. Hence, this is the required solution.
Force [kgms^-2] = mass [kg] x acceleration [ms^-2]
Work = force x distance
Work = [kgms^-2] x [m]
Work = [kgm^2s^-2]