Escape veolcity for Earth

The escape velocity of a particle on Earth is the minimum velocity required at Earth's surface in order that that particle can escape from Earth's gravitational field. Neglecting the resistance of the atmosphere, the system is conservative. From the conservation theorem for potential plus kinetic energyshow that the escape velocity for Earth, ignoring the presence of the Moon, is 11.2 km/s.
(Source: Herbert Goldstein, Classical Mechanics - Chapter 01)

Lets plug in the numbers to this simple problem:

This gives v = 11.2 km/s