Two 4.0kg masses are 1.0m apart on a frictionless table. each has 1.0μc of charge. part a what is the magnitude of the electric force on one of the masses?
what is the initial acceleration of each mass if they are released and allowed to move?

Electrostatic force = (Constant) x (charge-1) x (charge-2) / (distance²)

For all-SI units, the constant is almost exactly 9 x 10⁹ meter/farad.

So the force (on each mass) is

                   (9 x 10⁹) x (1.0 x 10⁻⁶) x (1.0 x 10⁻⁶) / (1.0)²  = 

                                               (9 x 1 x 1) x 10⁻³  /  (1)  = 

                                                       9 x 10⁻³  newtons .

To find the acceleration, use Newton's second law of motion: 

                                                                  Force  =  (mass) x (acceleration)

Divide each side by (mass):           Acceleration  =  (force) / (mass)

                                                       Acceleration  =  (9 x10⁻³) N / (4.0kg)

                                                       Acceleration  =    0.00225 meter/second²

If the charges have opposite signs, then the acceleration of each mass is
0.00225 m/s² in the direction toward the other one when you letum go. 
The force on each one, and therefore the acceleration, grows constantly,
as the distance between them shrinks.

If both charges have the same sign, then the acceleration of each mass is
0.00225 m/s² in the direction away from the other one when you letum go. 
The force on each one, and therefore the acceleration, shrinks constantly,
as the distance between them grows.

Answertraveling around a circular trackexplanation"traveling around a circular track" is the best answer as you could be traveling around a circular track at a constant speed. your velocity would therefore have the same magnitude but will always be constantly direction. since acceleration is the rate of change of velocity, the rate of change will only involve the direction of velocity and not the magnitude.wrong choices: "an object at rest" does not accelerate at all"increasing speed while traveling around a curve" means that the acceleration will not be constant due to only change in direction; it will be constant due to both magnitude and direction"an object in free fall" does not necessarily change direction