Question

Two charges of `-1 C` and `-3 C` are positioned on a line at points `-2` and `-4`, respectively. What is the net force on a charge of `-3 C` at `1`?

Answer 1

`0.8k` units

Explanation:

Click here for the diagram:

http://tube.geogebra.org/student/m2356805

The resultant force will be the vector sum of the forces due to the other two particles.

`stackrel(rarr)(F_("res"))=stackrel(rarr)(F_(31))+stackrel(rarr)(F_(32)`

Using Coulomb's Law:

`stackrel(rarr)(F_(31))=k.(3xx3)/(5^2)=(k.9)/25`

`stackrel(rarr)(F_(32))=k.(2xx2)/(3^2)=(k.4)/9`

`:.stackrel(rarr)(F_("res"))=(k.9)/25+(k.4)/9`

`stackrel(rarr)(F_("res"))=k0.8`

If the units of length were in metres then `k=9xx10^(9)"m/F"` and the result would be in Newtons.

The +ve sign means the force acts in the +ve direction i.e left to right.