Cuánto tiempo se tarda un carro si recorre una distancia de 20 metros con una velocidad de 25m/h

the independent variable, the one that is intentionally manipulated, is whether or not the car hits the barrier.

the dependent variable, the one that you measure the response in, is the distance that the washers travel.

this would be about 43%

electric field is a function of 1/r^2

yes, the force per unit charge for a point charge is inverse square law.