OPTIONS :
A.) the force that the ball exerts on the wall
B.) the frictional force between the wall and the ball
C.) the acceleration of the ball as it approaches the wall
D.) the normal force that the wall exerts on the ball
Answer: D.) the normal force that the wall exerts on the ball
Explanation: The normal force acting on an object can be explained as a force experienced by an object when it comes in contact with a flat surface. The normal force acts perpendicular to the surface of contact.
In the scenario described above, Erica's tennis ball experiences an opposite reaction after hitting the wall.This is in relation to Newton's 3rd law of motion, which states that, For every action, there is an equal and opposite reaction.
The reaction force in this case is the normal force exerted on the ball by the wall perpendicular to the surface of contact.
<span>The distance between two objects is increased by three times the oringinal distance. Since they were already separated by one time the original distance,
the additional three times the oringinal distance now puts them four times the original distance apart.
Whether we're talking about the gravitational forces of attraction or
the electrical forces of attraction, either one is inversely proportional
to the square of the distance between the objects.
So changing the distance to four times the original distance causes
the forces to become 1/4</span>² as strong as they were originally.
The forces become 1/16 of their original magnitude.<span>
</span>
The electrostatic force between the two ions is 
Explanation:
The electrostatic force between two charged particle is given by Coulomb's law:

where
is the Coulomb's constant
are the two charges
r is the separation between the two charges
In this problem, the ion of sodium has a charge of

while the ion of chlorine has a charge of

And the distance between the two ions is

Substituting, we find the electrostatic force between the two ions:

where the negative sign simply means that the force is attractive, since the two ions have opposite charge.
Learn more about electrostatic force:
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The ideal mechanical advantage (IMA) can be determined by the following equation:
IMA= Input distance/Output distance
The Input distance and Output distance are:
Input distance=220 meters
Output distance=110 meters
When you substitute in the equation of the ideal mechanical advantage (IMA), you obtain:
IMA= Input distance/Output distance
IMA= 220 meters/110 meters
IMA=2