# A charge of 7 C is at the origin. How much energy would be applied to or released from a  5 C charge if it is moved from  (6, -1 )  to (-9 ,-6 ) ?

Mar 17, 2018

The energy released is $= 22.7 \cdot {10}^{9} J$

#### Explanation:

The potential energy is

$U = k \frac{{q}_{1} {q}_{2}}{r}$

The charge ${q}_{1} = 7 C$

The charge ${q}_{2} = 5 C$

The Coulomb's constant is $k = 9 \cdot {10}^{9} N {m}^{2} {C}^{-} 2$

The distance

${r}_{1} = \sqrt{\left({6}^{2} + {\left(- 1\right)}^{2}\right)} = \sqrt{37} m$

The distance

${r}_{2} = \sqrt{{\left(- 9\right)}^{2} + {\left(- 6\right)}^{2}} = \sqrt{117}$

Therefore,

${U}_{1} = k \frac{{q}_{1} {q}_{2}}{r} _ 1$

${U}_{2} = k \frac{{q}_{1} {q}_{2}}{r} _ 2$

$\Delta U = {U}_{2} - {U}_{1} = k \frac{{q}_{1} {q}_{2}}{r} _ 2 - k \frac{{q}_{1} {q}_{2}}{r} _ 1$

$= k \left({q}_{1} {q}_{2}\right) \left(\frac{1}{r} _ 2 - \frac{1}{r} _ 1\right)$

$= 9 \cdot {10}^{9} \cdot \left(\left(7\right) \cdot \left(5\right)\right) \left(\frac{1}{\sqrt{117}} - \frac{1}{\sqrt{37}}\right)$

$= - 22.7 \cdot {10}^{9} J$

The energy released is $= 22.7 \cdot {10}^{9} J$