Grain is pouring into a silo to be stored for later use. Due to the friction between pieces of grain as they rub against each other during the pouring process, one piece of grain picks up a charge of 6.0 E -10 C and another piece of grain picks up a charge of 2.3 E -15 C. What is the electric force between them if the pieces of grain are 2 cm apart?

F = 3.105 10⁻²⁰ N

Explanation:

For this exercise let's use Coulomb's law

          F = k q₁ q₂ / r²

in this case each of the grains has a charge

         q1 = 6.0 10⁻¹⁰ C

         q2 = 2.3 10⁻¹⁵ C

and they are separated by a distance r = 2 cm = 0.02 m

let's substitute

          F = 9 10⁹ 6.0 10⁻¹⁰ 2.3 10⁻¹⁵ / 0.02²

         F = 3.105 10⁻²⁰ N

pe = weightxheight = 2000x1000=2,000,000joules