The electric field strength is inversely related to the square of the distance.so the strength of the electric field is given by
Here, 
is constant depend upon medium and its value is 
and q is charge and r is the distance.
Given 
and we know the charge of proton, 
.
Therefore,
Answer:
The principle of conservation of energy and angular momentum
Explanation:
At point A, the car experienced maximum of potential energy
As it moves down the hill, the potential energy decreases while the kinetic energy increases.
The maximum kinetic energy of the car is needed for the attainment of enough centripetal force to help the car move through the loop without falling .
First off, you need to know the weight of the projectile, lift and drag coefficients something like a high Reynolds number is preferred, then use the gravitational constant of 9.8 meters per second squared those would be a good start to get closer to your goal
