To solve this problem we will apply the concepts related to electric potential and electric potential energy. By definition we know that the electric potential is determined under the function:

= Coulomb's constant
q = Charge
r = Radius
At the same time

The values of variables are the same, then if we replace in a single equation we have this expression,

If we replace the values, we have finally that the charge is,




Therefore the potential energy of the system is 
To solve this problem it is necessary to apply the concepts related to the Period based on gravity and length.
Mathematically this concept can be expressed as

Where,
l = Length
g = Gravitational acceleration
First we will find the period that with the characteristics presented can be given on Mars and then we can find the length of the pendulum at the desired time.
The period on Mars with the given length of 0.99396m and the gravity of the moon (approximately
will be



For the second question posed, it would be to find the length so that the period is 2 seconds, that is:



Therefore, we can observe also that the shorter distance would be the period compared to the first result given.
The answer is A The waves filter ice from food
D. How high do the sound waves go