I'm confused about the answer given for question 6 in exercises A1. The question says "indicated air speed is proportional to:" and lists several options. The correct answer is given as "(c) the kinetic energy of the free airstream". But I don't think this is right. The dynamic pressure is equal to the kinetic energy (per unit volume), P = (1/2) rho V^2, where rho is the density of air and V is the true airspeed. The indicated airspeed is calculated (mechanically by the ASI) by finding the speed V that would be needed to produce the same dynamic pressure P if using air at sea level, IAS = sqrt(2*P/rho0) where rho0 is the density of air at sea level. So IAS is not proportional to kinetic energy (1/2) rho V^2. I don't think IAS is proportional to any of the options listed in the question.
The stem of the questions say says 'is proportional to' not 'is equal to'. It is proportional to, or 'varies with' the kinetic energy of the passing airflow. Any change is mass per unit volume or true airspeed will cause a corresponding change in the IAS.
Thank you for clarifying, Bob.
Many people would interpret the word 'proportional' in a narrower sense: x and y are proportional if y = a * x where a is a constant, so that y is doubled when x is doubled. (e.g. see the Wikipedia page for 'Proportionality (mathematics)'.) In this narrower sense, IAS is not proportional to the kinetic energy, but is proportional to the square root of the kinetic energy; IAS is 'directly related' to or 'is a function of' the kinetic energy.
I'm happy to use the wider meaning of 'proportional' that Bob has described, and I guess this will re-appear in other places in the CPL books (which are great, by the way!)
The important question is whether CASA CPL exams are likely to use this wider meaning..
I can promise you that CASA will accept the wider meaning. However I have changed the wording of the question to say 'is a function of' instead of 'is proportional to'.
Thanks for your feedback.
