Posted by **Maria** on Wednesday, January 23, 2013 at 11:16am.

Two iron spheres each have a volume of 10 cm^3 and a mass of 78g. How many electrons must be placed on each sphere so that the electrostatic force of repulsion between them just balances the force of gravitational attraction? Assume the distance between the spheres is more than 2 meters.

- Physics HELP!! -
**drwls**, Wednesday, January 23, 2013 at 12:45pm
You can treat the spheres as point charges at R >2m separation. If e is the charge on each sphere, for the electrical repulsion to equal the gravitational attraction,

G M^2 /R^2 = k Q^2/R^2

GM^2 = k Q^2

G is the Newton gravity constant and k is the Coulomb law constant

Solve for Q. The number of electrons is Q/e.

e is the elctron charge.

## Answer This Question

## Related Questions

- Physics - Two iron spheres each have a volume of 10 cm^3 and a mass of 78g. How ...
- Physics - Two insulated charged metallic spheres A & B have their centres ...
- physics - how many excess electrons must be placed on each of two small metal ...
- Physics - Two small spheres spaced 20.0 centimeters apart have equal charge. How...
- Physics - Two very small spheres are initially neutral and separated by a ...
- Physics - 1. The electrostatic force of attraction between two small spheres ...
- physics - Two spheres are placed so that their centers are 2.6 meters apart. The...
- physics - 1.) A small sphere of charge 2.4 μC experience a force of 0.36 N ...
- physics - Two spheres are placed so that their centers are 2.9 m apart. The ...
- Physics - Two electrically-charges spheres are suspended from insulated threads ...

More Related Questions