Your grade will probably go down to a D 68% or little higher than that
the electric force decreases because the distance has an indirect relationship to the force
Explanation:
The electric force between two objects is given by

where
k is the Coulomb's constant
q1 and q2 are the charges of the two objects
r is the distance between the two objects
As we can see from the formula, the magnitude of the force is inversely proportional to the square of the distance: so, when the distance between the object increases, the magnitude of the force decreases.
The period of the pendulum is 8.2 s
Explanation:
The period of a simple pendulum is given by the equation:

where
L is the length of the pendulum
g is the acceleration of gravity
T is the period
We notice that the period of a pendulum does not depend at all on its mass, but only on its length.
For the pendulum in this problem, we have
L = 16.8 m
and
(acceleration of gravity)
Therefore the period of this pendulum is

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X-rays and gamma rays are the only electromagnetci waves with a shorter wavelength, gamma rays being the smallest. Hope this helps ;)