Sledding is one of many favored winter evetns. But, there's alot fo physics that goes behind it. For starters, the friction going down the snowy hill will be minimal due to the plasic on an icy surfact. THis will allow you to go much faster due to a lesser amount of friction. If you wanted to calculate the amount of friction u just have to remember "friction is fun" and use Ff=uFn. If you wanted to get the fastest speed you should also take into account your distance, start velocity, the hill slope and your total mass. A heavier mass will weigh you down but depenign on your other factors that could be a benefit and help you out. If the distance is long enough you could gain a greater acceleration but it will become constant after a while. Because you must take into account friction as your outside force, you will stop sooner then you thought but it'd still be best to stay away from objects in your way.