A parachutist jumps from a plane. Beginning at the point when she reaches terminal velocity, which of the following is/are true? I. The jumper is in translational equilibrium. II. The jumper is not being acted upon by any forces. III. There is an equal amount of work being done by gravity and air resistance.
Correct answer: B. I and III only
- A. I only
- B. I and III only
- C. II and III only
- D. I, II, and III
Explanation
At terminal velocity, the parachutist is in translational equilibrium (statement I) because the net force acting on her is zero; the downward gravitational force is exactly balanced by the upward air resistance. This balance of forces results in a constant velocity. Statement II is false; the parachutist is indeed acted upon by forces, but they are balanced. Statement III is true because the gravitational force (doing work to move the jumper downward) is balanced by the work done by air resistance (which acts in the opposite direction). Therefore, the correct answer is B: I and III only.
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