Oop i have no clue but i need to answer questions so that i can ask some :)
<h3><u>Answer;</u></h3>
The period of the wave is <u><em>4 seconds</em></u>
<h3>
<em><u>Explanation;</u></em></h3>
- <em><u>The period of a wave or periodic time is the time taken for one complete oscillation to occur.</u></em> In this case, one complete oscillation occurs when the wave moves from one crest to the next or a trough to the next. <em><u>This takes 4 seconds. Therefore the period is 4 seconds.</u></em>
- <em><u>Frequency on the other hand is the number of oscillations by a wave in one second. Thus, f = 1/T, that is frequency is the reciprocal of periodic time.</u></em>
Here, you can derive that by numerical method, as follows:
F = m.a
m = F/a
So, here we can see when we decrease one, other increase by same effect; we can say they are "Indirectly Proportional" to each other!
Hope this helps!
Answer:

where E = electric field intensity
Explanation:
As we know that plastic ball is suspended by a string which makes 30 degree angle with the vertical
So here force due to electrostatic force on the charged ball is in horizontal direction along the direction of electric field
while weight of the ball is vertically downwards
so here we have


since string makes 30 degree angle with the vertical so we will have





where E = electric field intensity