(a) Determine the change in electric potential energy of a system of two charged objects when a -1.5-C charged object and a -4.0-C charged object move from an initial separation of 500 km to a final separation of 100 km. (b) What other quantities can you calculate using this information?

a)

b) Electric force

Explanation:

a)

The electric potential energy of a system of charge is given by

where:

is the Coulomb's constant

are the two charges

r is the separation between the two charges

In this problem, we have:

(1st charge)

(2nd charge)

The initial distance is

So the initial potential energy is

Later, the distance is decreased to

So the final potential energy is

Therefore, the change in electric potential energy is:

b)

There are several other quantities that we can calculate for this system of charges; for example, we can calculate the magnitude of the electric force between them.

The electric force between two charges is given by

where:

is the Coulomb's constant

are the two charges

r is the separation between the two charges

So at the beginning, when the distance is

The force is

While later, when the distance is

The force is

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