A point-like mass moves horizontally between two walls on a frictionless surface with initial kinetic energy E. With every collision with the walls, the mass loses 1 / 2 its kinetic energy to thermal energy. How many collisions with the walls are necessary before the speed of the mass is reduced by a factor of 8 ?
Answer Choices
A. 3
B. 4
C. 6
D. 8
E. 16