A block of mass \(m\) is released from rest at the top of a ramp inclined at an angle \(\theta\) above the horizontal. As the block slides down the ramp, the coefficient of kinetic friction between the block and the ramp varies with distance \(x\) from the release point according to \(\mu_k(x) = cx\), where \(c\) is a positive constant. Which of the following expressions represents the speed of the block after it has traveled a distance \(L\) down the ramp, assuming it does not come to rest beforehand?