Asmall cork with an excess charge of +6.0µc is placed 0.12 m from another cork, which carries a charge of -4.3µc.
a) what is the magnitude of the eletric force between the corks?
b) is this force attractive or repulsive?
c) how many excess electrons are on the negative cork?
d) how many electrons has the postive cork lost?

A) 16.1 N

The magnitude of the electric force between the corks is given by Coulomb's law:

where

k is the Coulomb's constant

is the magnitude of the charge on the first cork

is the magnitude of the charge of the second cork

r = 0.12 m is the separation between the two corks

Substituting numbers into the formula, we find

B) Attractive

According to Coulomb's law, the direction of the electric force between two charged objects depends on the sign of the charge of the two objects.

In particular, we have:

- if the two objects have charges with same sign (e.g. positive-positive or negative-negative), the force is repulsive

- if the two objects have charges with opposite sign (e.g. positive-negative), the force is attractive

In this problem, we have

Cork 1 has a positive charge

Cork 2 has a negative charge

So, the force between them is attractive.

C)

The net charge of the negative cork is

We know that the charge of a single electron is

The net charge on the negative cork is due to the presence of N excess electrons, so we can write

and solving for N, we find the number of excess electrons:

D)

The net charge on the positive cork is

We know that the charge of a single electron is

The net charge on the positive cork is due to the "absence" of N excess electrons, so we can write

and solving for N, we find the number of electrons lost by the cork:

potential energy is directly proportional to height.

more height = more potential energy.

greatest increase in height = greatest increase in potential energy

where are the points with the greatest increase in height ?

has to be c-e or d-e .

no sign of dia of fuel cell