You go sledding with your little brother to a hill that has a relatively constant slope oriented at an angle of = 15 above the horizontal. You are worried that your little brother will be going too fast before the slope mellows out which is roughly at a distance of L = 20 m away from his starting point. Being the good sibling that you are, you decide to calculate his speed at the bottom (fun!) before allowing him to go. Doing a quick google search you find out that the coefficient of kinetic friction between polished wood and snow is 0.14, which is pretty low, so you decide to use it to do the calculation.

What is the speed at the bottom?