Proportionality calculations (Coulombs Law)

[whitestrat]

Two unlike charges attract each other with a force of 5 x 10^-5 when placed 12 cm apart.



1) What is the force between them when they are 4.0cm apart


2)At what distance apart will the force between them be 2.0 x 10^-4


now i have attempted these questions, but i cannot find a suitable method of solving these questions that is consistent with all types of these questions...
Can anyone be willing to show me a method of solving these types of questions.

 

[kamerling]

Two unlike charges attract each other with a force of 5 x 10^-5 when placed 12 cm apart.

1) What is the force between them when they are 4.0cm apart

2)At what distance apart will the force between them be 2.0 x 10^-4

now i have attempted these questions, but i cannot find a suitable method of solving these questions that is consistent with all types of these questions...
Can anyone be willing to show me a method of solving these types of questions.

you know Coulombs Law?

F = \frac { k q_1 q_2 }{r^2}

In this problem you have F = 5 x 10^-5 N if r = 5 cm. What would F be if r = 4.0 cm

 

[whitestrat]

yes i know coulombs law, its just the question is worked out using proportionality from coulombs law

 

[alphysicist]

Hi whitestrat,

Coulomb's law is an inverse square law, so, for example, if you double the distance between the charges the force decreases by a factor of four; if you halve the distance, the force increases by a factor of four.

Here the distance goes from 12cm to 4cm. So what happens to the force?