The Physics of Tobogganing Part 2

With a wind chill temp of -18 degrees Celsius, it was a perfect day for sledding (right). On our last day (*tear*), my siblings and I spent two hours tobogganing in Hamstead Park with my cousin. As expected, my cousin was pretty tired at the end (as the picture below illustrates) and was more than ready for lunch. 

This scenario reminds me of a really old concept of physics: WORK. As my uncle pulls my cousin, he is peforming work. Because my uncle is pulling my cousin at an angle, the work equation in this case is as follows: W=F(net)xcos(theta). Assuming my uncle is exerting a constant force F at a distance x at an angle theta, then this is an accurate equation. The forces in this case include weight mg of my cousin and the sled, which is cancelled by the normal force N, the friction force F(f) caused by the contact between the snow and the sled which goes in the opposite direction and counteracts the force F exerted by my uncle. However, since the system is moving in the direction of my uncle, the force F must be greater than force F(f) in order to produce this net motion. If my uncle pulled my cousin in such a manner that the angle between force F and theta is 0 (which is 1), then the equation would be W=F(net)x and my uncle would have needed to exert less force.