Mechanical Aptitude Flashcards

If Gear 1 turns clockwise as indicated by the arrow, which of the following statements is true about Gear 3 and Gear 4?

Answer: Gear 3 turns counter-clockwise, and Gear 4 turns clockwise.

When two gears mesh, they always turn in opposite directions. Since Gear 1 turns clockwise, Gear 2 (the idler gear) must turn counter-clockwise. Because Gear 2 turns counter-clockwise, Gear 3 must turn clockwise. Finally, since Gear 3 turns clockwise, Gear 4 must turn counter-clockwise.

A firefighter is using a pulley system to hoist a salvage cover weighing 100 lbs to a roof. The system consists of one fixed pulley at the top and one movable pulley attached to the load. Ignoring friction, what is the approximate force required by the firefighter to lift the cover?

Answer: 50 lbs

The mechanical advantage of a pulley system is determined by the number of rope segments supporting the load. In a system with one fixed and one movable pulley, two rope segments support the load. This provides a mechanical advantage of 2, which means the force required is halved. Therefore, 100 lbs / 2 = 50 lbs of force is needed.

To achieve the greatest mechanical advantage when using a halligan tool to pry open a door, where should the firefighter apply force?

Answer: As far from the fulcrum as possible, at the end of the handle.

A halligan tool used for prying functions as a Class 1 lever, where the fulcrum is between the effort and the load. To maximize mechanical advantage (the amplification of force), the effort should be applied as far away from the fulcrum as possible. This increases the length of the effort arm, requiring less force to move the load.

A pumper is supplying a hose line to firefighters on the 5th floor of a building. If the pump operator increases the engine pressure, what is the primary effect on the water being delivered?

Answer: The velocity and reach of the water stream will increase.

Engine pressure is the force pushing water through the hose system. Increasing this pressure directly increases the velocity at which the water exits the nozzle. This results in a more powerful stream that can travel a greater distance (reach), which is necessary to overcome gravity and friction loss when pumping to elevated floors.

Which of the following actions would increase the stability of an extension ladder that is set up against a building?

Answer: Widening the base of support by moving the base further from the wall (to a proper 4:1 ratio).

The stability of an object is increased by widening its base of support and lowering its center of gravity. Moving the base of the ladder further from the wall (up to the recommended 75-degree angle or 4-to-1 ratio) widens its base of support, making it more stable and less likely to tip sideways. An angle that is too steep makes it more likely to tip backward.

If the small gear with 15 teeth makes 4 complete rotations, how many rotations will the large gear with 60 teeth make?

Answer: 1 rotation

The relationship between two meshed gears is inversely proportional to their number of teeth. The gear ratio is 60:15, which simplifies to 4:1. This means the small gear must turn 4 times to make the large gear turn once. Since the small gear rotates 4 times, the large gear will complete exactly 1 rotation (4 rotations / 4 = 1 rotation).