2 The sum of two point charges is 6 C. They attract each other with a force of 0.9 N, when kept 40 cm apart. Calculate the charges.

Consider a system to be two train cars traveling toward each other. what is the total momentum of the system before the train cars collide?   kg • what must the total momentum of the system be after the train cars collide?   kg •  

This is for my 8th grade science class, i really don’t understand. can someone me? , lol.

What is a view of science and psychology that says the value of knowledge depends on its usefulness? a. pragmatism b. psychotherapy c. physiology