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A helicopter's engine cannot both lift the craft and quickly restore the blades' rotational kinetic energy because of:
AFuel freezing in flight
BWeight limitations on the engine
CThe blades being too short
DAir being too thin at altitude
Answer & Solution
Correct answer: B. Weight limitations on the engine
1. A helicopter stores a great deal of energy in its spinning blades.
2. If the blades slow, that store has to be replenished.
3. Because of weight limitations, helicopter engines are too small to supply both the energy needed for lift and to replenish the rotational kinetic energy of the blades once they have slowed down.
4. That is why autorotation landings depend on the blades keeping their spin.
5. If the altitude is too low, there is insufficient time for the blade to regain lift before reaching the ground.
_Source: OpenStax College Physics for AP(R) Courses 2e (CC BY 4.0), Ch 10 'Rotational Motion and Angular Momentum', sections 10.1-10.7_
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