Physics: Principles with Applications (7th Edition)

The pushing force is constant and the 2 displacements are the same. The same work is done by moving the block from A to B as by moving it from B to C. There is no friction, so this is the net work, and the same work results in the same change in kinetic energy. Therefore the KE at point C is exactly twice as great as it is at point B. However, kinetic energy depends on the square of the speed, so the speed at point C will be greater than the speed at point B by a factor of $\sqrt{2}$, not by a factor of 2.