Question

Two charged particles having charges $1$ and $-1$ $\mu$C and of mass $50$ g each are held at rest while their separation is $2$ m. Now the charges are released. Find the speed of the particles when their separation is $1$ m.

• A. $\frac{1}{5}m{s}^{-1}$
• B. $\frac{3}{5}m{s}^{-1}$
• C. $\frac{3}{10}m{s}^{-1}$
• D. $\frac{2}{7}m{s}^{-1}$

Answer 1

Answer: (C)

$\frac{3}{10}m{s}^{-1}$

Applying conservation of mechanical energy, we get

$(K.E.+P.E.{)}_{initial}=(K.E.+P.E.{)}_{final}$

initially charges are at rest so their kinetic energy will be zero and let finally they are moving with speed v

$\frac{-9\times {10}^9\times {10}^{-12}}{2}=\frac{-9\times {10}^9\times {10}^{-12}}{1}+\frac{1}{2}\left(2m\right)v^2$

or

$v=3/10m{s}^{-1}$