A large solid sphere with uniformly distributed positive charge has a smooth narrow tunnel through its centre. A small particle with negative charge, initially at rest far from the sphere, approaches it along the line of the tunnel, reaches its surface with a speed v, and passes through the tunnel. Its speed at the centre of the sphere will be ?

An extensive strong circle with consistently conveyed positive charge has a smooth thin passage through its middle. A little molecule with negative charge, at first very still a long way from the circle, approaches it along the line of the passage, achieves its surface with a speed v, and goes through the passage. The speed at the focal point of circle will be zero.