Mechanical Reasoning Principles Questions and Answers Flashcards

A pulley system is used to raise a 300-pound victim. If the system has a mechanical advantage of 3, how much force must the rescuer apply (ignoring friction)?

Answer: 100 lbs

Force equals load divided by mechanical advantage: 300 divided by 3 equals 100 pounds.

Which simple machine does a firefighter use when sliding a victim down a stairway on a rescue sled?

Answer: Inclined plane

An inclined plane reduces the force needed to move a load through a vertical height by spreading the work over a longer distance.

In a compound pulley system, if you must pull 6 feet of rope to raise a load by 1 foot, what is the mechanical advantage?

Answer: 6

Mechanical advantage equals effort distance divided by load distance: 6 divided by 1 equals 6.

A fire pump impeller spins faster when driven by a larger sprocket connected by a chain to a smaller sprocket on the impeller shaft. Which sprocket is the driver?

Answer: The larger sprocket — it drives at lower RPM but speeds up the smaller driven sprocket

A large driver sprocket connected to a small driven sprocket increases the output RPM on the driven shaft, the same principle as a favorable gear ratio.

What is the main advantage of a worm gear mechanism used in some fire apparatus equipment?

Answer: Large mechanical advantage combined with a self-locking ability

Worm gears provide high gear reduction (large mechanical advantage) and are self-locking — the worm drives the gear wheel but the gear wheel cannot back-drive the worm.

A fire department come-along (ratchet lever hoist) is rated at 2,000 pounds. The device uses which mechanical principle to achieve this rating?

Answer: Ratchet and pawl combined with a lever arm to provide mechanical advantage

A come-along uses a ratchet mechanism to hold position and a lever arm to multiply input force, allowing one person to move heavy loads.