Answer:
We can relate the kinetic energy of the particle to the potential difference between the plates by following equations:
Work energy theorem:




So,

If the distance is doubled and the potential difference is halved, then

Explanation:
As can be seen from the relationship between kinetic energy and the potential difference, the distance between the plates has no effect on the relation between kinetic energy and the potential difference. Since the charge of the second particle is equal to that of the first one, the new kinetic energy would be half of the first kinetic energy.
The position function x(t) of a particle moving along an x axis is 
a) The point at which particle stop, it's velocity = 0 m/s
So dx/dt = 0
0 = 0- 12t = -12t
So when time t= 0, velocity = 0 m/s
So the particle is starting from rest.
At t = 0 the particle is (momentarily) stop
b) When t = 0

SO at x = 4m the particle is (momentarily) stop
c) We have 
At origin x = 0
Substituting

t = 0.816 seconds or t = - 0.816 seconds
So when t = 0.816 seconds and t = - 0.816 seconds, particle pass through the origin.
When the relationship between two variables are said to be proportional, it means that one variable is a constant multiple of the other variable. They are related by a constant of proportionality, usually denoted as k.
In this problem, the dependent variable is the distance in kilometers. Your mileage is limited with the amount of fuel you have. Thus, the independent variable is the liters of fuel. When these two are proportional, it could be expressed as
distance = k * liters of fuel, such that
distance/liters of fuel = k
By variation,
distance,1/liters of fuel,1 = distance,2/liters of fuel,2, where 1 denotes situation 1 and 2 denotes situation 2. Therefore,
999999 km /<span>999 liters = x km /</span><span>121212 liters, where x is the unknown distance. We can now therefore find the value of x.
x = (999999*121212)/999
x = 121333212 kilometers</span>