Two corrections with explicit signs
A fictional instrument worksheet states that the glider's total-energy vertical rate is minus 2 knots, where positive means upward. Its specified still-air polar sink is 3 knots downward at that operating point. The exercise uses a simplified model in which total-energy rate equals airmass vertical rate minus the positive still-air sink value. A learner calls the minus 2 reading proof that the surrounding air is sinking. Another applies the supplied correction to estimate airmass motion. The task asks for the arithmetic and the distinction between total-energy compensation and a netto estimate. It provides no actual instrument calibration, aircraft control instruction or thermal-centering maneuver. A sound answer retains the signs and acknowledges that a real estimate depends on the correct polar and compensation inputs.
1. Calculate the model airmass vertical rate.
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Minus 2 equals airmass rate minus 3. Therefore airmass rate is plus 1 knot upward. The glider can still descend while flying in air rising more slowly than its own sink.
2. Why is total-energy compensation alone insufficient?
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It reduces speed-height exchange effects but does not itself remove the glider's still-air sink. The supplied polar correction is a separate step in this model.