One hypothesis above would probably rely on the situation called <em>"inelastic collision." </em>The two carts are travelling towards each other at different speed. So, this means that once they collide, the kinetic energy will not be conserved but will be transferred as <em>sound energy, thermal energy or material deformation</em>. The impact will be great, thus a <u>greater fraction of kinetic energy will be lost from the system.</u>
By definition, the electric field is the force per unit charge created by a charge distribution.
If the charge creating the field is a point charge, the force exerted by it on a test charge, must obey Coulomb´s Law, so, it must be inversely proportional to the square of the distance between the charges.
So, if the distance increases twice, as the force is inversely proportional to the square of the distance, and the square of 2 is 4, this means that the magnitude of the force exerted on the test charge must be 4 times smaller.