Answer:
A) F=-20.16×10⁹N
B) if the distance doubles, force is 4 times smaller.
Explanation:
q1=-28C
q2=5mC=0.005C
d=25cm=0.25m
Electrostatic force between charges: F=k×q1×q2/d², where k is a coefficient that has the value k=9 × 10⁹ N⋅m²⋅C^(-2) for air.
Thus:
F=9×10⁹×(-28)×0.005/0.25²
F=-20.16×10⁹N
The minus sign indicates attraction.
If distance doubles, d1=2×d, then we have 4d² at the denominator and the force is 4 times smaller.
111.0 because 111.009 rounds off to 111.01, thus rounding again off to 111.0
For this case we have that according to Newton's second law it is true that:

Where:
F: It is the force
m: It is the mass
a: It is the acceleration
According to the data we have:

So, we have:

Thus, the applied force will be 7 Newtons.
Answer:

Constructive interference in performance halls and the elimination of echoes are reasons why choir concerts better in performance halls than in gymnasiums.
<h3>What is constructive interference?</h3>
Constructive interference is a phenomenon which occurs when two waves travelling in same direction and which are in phase add up together to produce a wave of greater amplitude.
Constructive interference occurs in performance halls while destructive interference occurs in gymnasiums.
Also in performance halls, echoes are minimized due to the padded walls and the curtains while echoes which disturb choir concerts occur in gymnasiums.
Therefore, choir concerts better in performance halls than in gymnasiums because of constructive interference in performance halls and the elimination of echoes.
Learn more about constructive interference and echoes at: https://brainly.in/question/2378717