6. (3 points) A skateboarder of mass m is riding along a frictionless ramp, as show in Figure. 3. Using the coordinate system shown in the Figure, the ramp can be modelled as being horizontal for negative values of x, and then a parabola, y(x) = a + bx + cx, for positive values of x. The ramp ends at x = x0. Show that the work done by gravity on the skateboarder over the path of the ramp (between x = 0 and x = xo) is given by: W = -mg(bx0+ cx) y 0 y(x) = a + bx + cx x Figure 3: A skateboarder on a ramp.