Two iron spheres are suspended from strings and
separated by a distance of 9.0 meters. The
charge on one sphere is 7.0*10^-8 Cand the other -3.0
*10^-5 C. What is the electric force on the spheres?
A. A repulsive force of 4.6*10^-4N
B. An attractive force of 2.3*10^-4 N
C. An attractive force of 4.6*10^-4 N
D. A repulsive force of 2.3*10^-4 N

B. An attractive force of 2.3*10^-4 N

Explanation:

As we know by Coulomb's law that the electrostatic force between two charges is given as

here we know that

r = 9.0 m

now we have

since both charges are opposite charges so they will attract each other by the force we calculated above so correct answer will be

B. An attractive force of 2.3*10^-4 N

what experimental evidence led scientists to change from the previous model to this one?

a few of the positive particles aimed at a gold foil seemed to bounce back.

the colors of light emitted from heated atoms had very specific energies.

experiments with water vapor showed that elements combine in specific proportions.

cathode rays were bent in the same way whenever a magnet was brought near them.