An open circuit means there is a break in the conducting path so the loop isn’t completed. Because there’s no closed path, current has no route to follow, so it cannot flow—even when a voltage source is connected. The voltage can still exist across the gap, but the current is effectively zero since the path’s resistance is infinite at the break. This aligns with I = V/R: with the path broken, current cannot pass. The other statements imply a closed loop or active current flow, which isn’t the case in an open circuit.

The main idea is that the tail rotor provides anti-torque to counter the twisting effect of the main rotor. In a single-rotor helicopter, the engine turns the large rotor, and by Newton’s third law the fuselage tends to spin in the opposite direction. The tail rotor pushes or pulls on the air to create a counteracting torque, keeping the helicopter from spinning and giving the pilot control of yaw by adjusting how much tail rotor thrust is produced. Lift and propulsion come from the main rotor and the drive system, respectively, while hover stability is achieved through this anti-torque action plus pilot input. In short, the tail rotor’s job is to cancel the main rotor’s torque so the aircraft can be steered and held steady.

The key idea is identifying the component that physically carries torque from the engine to the gearbox input. Drive shafts are designed to transmit rotational energy between connected parts, delivering power to each gearbox. They are the continuous link that makes the gearbox input rotate with the engine’s output. Clutches control engagement but aren’t the fixed power path to the gearbox. Bearings support rotating parts but don’t transfer torque. Transmission fluid lubricates and cools, not transmit power. Therefore, the drive shaft is the component that transmits rotational energy to its respective gearboxes.

The idea is recognizing which chemistry behaves most like a typical car battery—providing a strong, high current surge for engine cranking and being robust in the aviation environment. Hueys rely on a lead-acid battery for starting because it delivers the large burst of current needed to crank the engine, and it’s rugged, reliable, and easy to recharge with the aircraft’s electrical system. Lead-acid cells are built with lead plates in a sulfuric acid electrolyte, a proven combination for starter duties and heavy vibration where a helicopter operates. The other chemistries don’t fit that car-battery performance profile: nickel-cadmium is lighter and has different discharge characteristics, dry cells aren’t capable of delivering the high current required for starting, and lithium-ion, while energy-dense, wasn’t the standard starter battery for Hueys and isn’t described as “works like a car battery.”