Earth exerts an electric force on small charged objects located near its surface. The effect can be modeled by assuming Earth is a particle at the center of Earth carrying a charge of \(-6.76 \times 10^{5} \mathrm{C}\).

(a) What is the magnitude of the electric force exerted by Earth on an electron at its surface? Is this force attractive or repulsive?

(b) How does this force magnitude compare with the magnitude of the gravitational force exerted by Earth on the electron?

(c) How much negative charge would you have to put on a penny in order for the repulsive electric force exerted by Earth on the penny to cancel the attractive gravitational force exerted by Earth on the penny?

(d) How many electrons would you have to add to the penny to achieve this?