# 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 ?

Dec 30, 2015

$0.8 k$ units

#### Explanation:

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:

$\stackrel{\rightarrow}{{F}_{31}} = k . \frac{3 \times 3}{{5}^{2}} = \frac{k .9}{25}$

$\stackrel{\rightarrow}{{F}_{32}} = k . \frac{2 \times 2}{{3}^{2}} = \frac{k .4}{9}$

$\therefore \stackrel{\rightarrow}{{F}_{\text{res}}} = \frac{k .9}{25} + \frac{k .4}{9}$

$\stackrel{\rightarrow}{{F}_{\text{res}}} = k 0.8$

If the units of length were in metres then $k = 9 \times {10}^{9} \text{m/F}$ and the result would be in Newtons.

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