I understand the confusion now. What they mean is that you're determining the shape of the mountain top using an equation, and then the skier is skiing along that mountain top according to gravity. But they don't say that.

Instead they say the task is to set path of skier - i.e. how the skier goes down the mountain. But that's not correct - the skier obviously doesn't need to just follow the mountain top. Common sense/reality is the opposite - you rarely just follow a mountain top.

If they'd just said the above, and I think not shown the value of t, it would have been a lot clearer, at least to me.

If in later levels they show formula(s) using gravity, and perhaps show the skier on different planets, with different values of G, then I can see the value in showing the value of t. But as it is, I think it's confusing.