Which statement best explains the relationship between electric force and the charges on two interacting objects? a. electrical force is directly proportional to the product of the charges on the two objects. b. electrical force is inversely proportional to the product of the charges on the two objects. c. electrical force is inversely proportional to the product of the squares of the charges on the two objects. d. electrical force is directly proportional to the product of the squares of the charges on the two objects.

Aparticle's position is given by x = 3.00 - 9.00t + 3t2, in which x is in meters and t is in seconds. (a) what is its velocity at t = 1 s? (b) is it moving in the positive or negative direction of x just then? (c) what is its speed just then? (d) is the speed increasing or decreasing just then? (try answering the next two questions without further calculation.) (e) is there ever an instant when the velocity is zero? if so, give the time t; if not, answer "0". (f) is there a time after t = 3 s when the particle is moving in the negative direction of x? if so, give the time t; if not, answer "0".