Question

A large solid sphere with uniformly distributed positive charge has a smooth narrow tunnel through its centers. A small particle with negative charge ,initially at rest far from sphere , approaches it along the line of the tunnel, reaches its surface with a velocity v,and passesthrough the tunnel. Find its speed at the center of the sphere.

Answer 1

$$\begin{gathered} Sincethenegativechargeisequallyattractedfromalldirections \\ oftheuniformlychargedsolidsphere,sothenegativecharge \\ moveswithvelocityveventhroughthecentreofthesolidsphere.. \end{gathered}$$