Hello L,
1. There are many types of forces in physics; however, if we are talking about free fall, we are specifically talking about the force due to gravity or in other words:
Fg = mg,
where g is always a constant (same) acceleration rate of 9.8m/s^2. I believe a. is the correct answer.
2. For the second part, its the same problem, but now we have another force, "air drag" and this force is equal and opposite of the force due to gravity, Fg. So if we use Newton's famous equation and sum the forces in the ydirection, we get a net acceleration equal to zero! (Acceleration due to air drag is a resistive force, so it acts in the direction opposite of motion). This means that the parachuist stops accelerating and this is also known as reaching "terminal velocity." The correct answer should be a.
7/1/2014

Alexander F.
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