Won't KE final BE qual to zero ?

But in reality skateboarder accelerate and make some jump with tricks higher and higher ... like tony hawk landed 900 or 1080 ... he is not landing this trick at the first run he need to accumulate some speed in order to succeed ... kzfaq.info/get/bejne/itSmg9eQxp3Nf4U.html , kzfaq.info/get/bejne/hbWXYJee2aeXiqM.html - I think human play with grativity and there position to vary the speed and their momemtum , it's not a static mini ball who keep the same position everywhere in the system... like you explained ... at the bottom of the half pipe the speed is higher or slower to depend what he want to do and the speed add up if the skateboarder want to accumulate speed for a bigger jump ... also there's some limits like in the video in order to landed an 1260 you need a mega ramp ...