I just took the technical test since I was curious (and it's been a *long* time since I took my L2), and I disagree with these two questions a bit:
For a subsonic rocket, what factors most greatly affect the coefficient of drag (Cd)?
- Speed, airframe dimensions, nosecone shape and fin shape.
Feedback: As speed increases, the drag number changes. The length and diameter of the rocket factors into the total surface area. The nose cone shape affects the airflow over the front of the nose cone. The fin shape and fin area factor into the total surface area.
For subsonic flight, the coefficient of drag actually tends to slightly decrease with speed, but overall it's reasonable to just model it as being constant. The drag
force increases, but until you get close to the speed of sound, Cd is close to fixed (and in fact that's a large part of why it's useful). Within reasonable reynolds number ranges, and below about mach 0.8 or so, rocket-shaped objects will have a drag coefficient basically only determined by shape and surface finish. The inclusion of "speed" is kind of misleading here, particularly in the context of specifying "subsonic" in the question.
In general terms, the specific impulse of a rocket motor is:
- The total impulse divided by a unit weight of propellant.
Feedback: Specific impulse is a term used to define the efficiency of a rocket propellant and is the total impulse derived from a unit weight of propellant.
The specific impulse of a rocket motor is not the total impulse divided by a unit weight of propellant. It's the total impulse divided by the
total weight of propellant in the motor, and is mathematically equivalent to the total impulse the motor would give if it only contained a single unit weight of propellant.
Overall though, it looks good, and it at least seems better than I remember the test being when I took it, though that was long enough ago that I'm not sure I remember the questions all that well to be honest.