Final answer:
The speed at which the pine cone impacts the ground is the same as if it would have hit something on its way down, which is 15 m/s. This is unchanged by the slope of the ground and is solely due to the gravitational force.
Step-by-step explanation:
The question is concerned with the principles of kinematics and gravitational acceleration in classical mechanics, which is a part of Physics. The scenario given is a pine cone falling straight down from a pine tree on a slope. In the absence of air resistance, the only acceleration affecting the pine cone is the acceleration due to gravity, which is approximately 9.8 m/s2. While the slope of the ground matters for where the pine cone lands, it does not affect the vertical speed of the pine cone when it hits the ground.
For objects thrown vertically upward or falling back down in Earth's gravity (ignoring air resistance), the speed at which they impact an object on the way down is the same as the speed at which they would have impacted it on the way up. Thus, referring to the provided reference information, which states that neglecting air resistance, the rock hitting or missing a coconut on the way down will have the same speed it would have if it had hit the coconut on the way up; it follows that the pine cone will hit the ground with the same speed it had when it fell, which is the final velocity just before impact - 15 m/s, assuming that is the speed with which it was falling under the force of gravity.