A bullet of mass $m$ and charge $q$ is fired towards a solid uniformly charged sphere of radius $R$ and total charge $+ q$. If it strikes the surface of sphere with speed $u$, find the minimum speed $u$ so that it can penetrate through the sphere. (Neglect all resistance forces or friction acting on bullet except electrostatic forces)
A bullet of mass $m$ and charge $q$ is fired towards a solid uniformly charged sphere of radius $R$ and total charge $+ q$. If it strikes the surface of sphere with speed $u$, find the minimum speed $u$ so that it can penetrate through the sphere. (Neglect all resistance forces or friction acting on bullet except electrostatic forces)
- A
$\frac{q}{{\sqrt {2\pi {\varepsilon _0}mR} }}$
- B
$\frac{q}{{\sqrt {4\pi {\varepsilon _0}mR} }}$
- C
$\frac{q}{{\sqrt {8\pi {\varepsilon _0}mR} }}$
- D
$\frac{{\sqrt 3 \,\,q}}{{\sqrt {4\pi {\varepsilon _0}mR} }}$
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