일반물리학 2 — Electric Potential: Problem 39

39 (a) What is the escape speed for an electron initially at rest on the surface of a sphere with a radius of 20 cm and a uniformly distributed charge of \(1.6 \times 10^{-15}\) C? That is, what initial speed must the electron have in order to reach an infinite distance from the sphere and have zero kinetic energy when it gets there? (b) If its initial speed is twice the escape speed, what is its kinetic energy at infinity?