Discussion
Dynamic pressure at \( 60 \ \mathrm{m/s} \) is \( 2205 \ \mathrm{Pa} \) at sea level density. At \( 45 \ \mathrm{m/s} \) it is approximately
Answer: C
Correct answer: 1240 Pa
Dynamic pressure varies with the square of speed at constant density:
\[ q = \tfrac{1}{2}\rho V^{2} \qquad \frac{q_2}{q_1} = \left(\frac{V_2}{V_1}\right)^{2} \]
\[ q_2 = 2205 \times \left(\frac{45}{60}\right)^{2} = 2205 \times 0.5625 = 1240\ \mathrm{Pa} \]
The square law is why every aerodynamic control weakens so sharply as speed falls: dropping to three-quarters of the speed leaves only nine-sixteenths of the moment. That is precisely the difficulty at minimum control speed, where the asymmetric thrust to be balanced has not fallen at all.
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