An electron enters a linear accelerator with a speed v=10m-s.A vertical section of the accelerator tube is shown in the figure, where the lengths of the successive sections are designed such that the electron takes the same time >=20ms to traverse each section. If the momentum of the electron increases by 2% every time it crosses the narrow gap between two sections, what is the length (in km) of the collider which will be required to accelerate it to 100 km-s?