During heavy exercise, muscle cells use oxygen more quickly than normal. Which system responds by carrying extra oxygen to these muscle cells? a. digestive b. circulatory c. nervous
d. immune

The answer is 4f======since electrostatic force is given by    we let f be the electrostatic force when  r = 1 m    if we let  denote the electrostatic force when the distance is decreased so that r = 0.5m, then    we established earlier that f = kq₁q₂. therefore    the force will now be 4f.

Your answer would be b. the total kinetic and potential energies of its particles