FCTC Test Applying Mechanical Reasoning Questions and Answers 2 — Questions and Answers
Question 1: A Halligan bar is used to pry open a door. The firefighter applies force 18 inches from the fulcrum point at the door frame. What simple machine principle does this demonstrate?
- Wheel and axle
- First-class lever (Correct answer)
- Inclined plane
- Pulley system
Correct answer: First-class lever
A Halligan bar acting against a door frame with the contact point as the fulcrum and the firefighter applying force at the far end is a classic first-class lever.
In a first-class lever, the fulcrum is positioned between the effort and the load. The Halligan bar's fork contacts the door frame (fulcrum), and the firefighter's force at the handle end multiplies the force applied at the lock point. This mechanical advantage is why forcible entry tools are designed with long handles.
Question 2: Two firefighters carry a victim on a stretcher, each holding one end. How is the load distributed between them on level ground?
- The larger firefighter bears the entire load
- Each firefighter bears approximately half the total load (Correct answer)
- The rear firefighter bears most of the load due to gravity
- The front firefighter bears significantly more load than the rear
Correct answer: Each firefighter bears approximately half the total load
On level ground, each person supporting equal distances from the center of mass bears approximately half the load.
When two carriers support a load at equal points on either side of the center of mass on level ground, each bears half the total load. When ascending stairs the rear carrier actually supports more of the weight because they are lower. Understanding load distribution helps prevent back injuries during patient movement.
Question 3: A hydraulic door ram forces entry. The device operates on which principle?
- Bernoulli's principle of fluid flow
- Pascal's Law — fluid pressure transmits force equally in all directions (Correct answer)
- Newton's third law only
- Archimedes' principle of buoyancy
Correct answer: Pascal's Law — fluid pressure transmits force equally in all directions
Hydraulic door rams apply Pascal's Law — fluid pressure is transmitted equally in all directions, allowing a small pump to generate large output forces.
Pascal's Law states that pressure applied to an enclosed fluid is transmitted undiminished in all directions. Hydraulic rams concentrate this pressure on a piston to produce enormous output force from a compact device. This same principle drives hydraulic rescue tools such as the Jaws of Life.
Question 4: A firefighter uses a come-along attached to a vehicle to move it off a victim. If the come-along provides 4:1 mechanical advantage and the vehicle requires 2,000 pounds to move, how much force must the firefighter apply?
- 250 lbs
- 500 lbs (Correct answer)
- 1,000 lbs
- 2,000 lbs
Correct answer: 500 lbs
Force equals load divided by mechanical advantage: 2,000 divided by 4 equals 500 pounds.
With 4:1 mechanical advantage, the firefighter applies 2,000 divided by 4 equals 500 pounds. Friction in the rope and pulley system reduces real-world efficiency somewhat, so actual effort will be slightly more. Come-alongs are rated for their maximum load capacity, not their required input force.
Question 5: A ventilation fan is positioned at a doorway. As the blade diameter increases while RPM stays constant, what happens to airflow volume (CFM)?
- CFM decreases
- CFM remains constant
- CFM increases (Correct answer)
- CFM is unrelated to blade diameter
Correct answer: CFM increases
Larger fan blades sweep a greater area per revolution, moving more air volume per unit time at the same rotational speed.
Airflow in CFM is proportional to blade swept area times rotational speed times pitch factor. Increasing blade diameter increases the swept area, so more air is moved per revolution. Fire department positive pressure ventilation fans are sized with large blade diameters to maximize CFM for rapid smoke removal.
Question 6: A roof ladder is hooked over a ridge and a firefighter hangs from it. What type of load does the hook experience?
- Compressive load
- Tensile load (Correct answer)
- Shear load
- Torsional load
Correct answer: Tensile load
The firefighter's weight pulls the hook downward, placing it under tension — a pulling or stretching force.
Tensile loads stretch a material along its axis. The roof ladder hook bears the firefighter's weight as a downward pull, creating tension in the hook and upper rungs. Roof ladder hooks are designed and tested to specified tensile load ratings per NFPA 1931.
FCTC Test Applying Mechanical Reasoning Questions and Answers 2
A Halligan bar is used to pry open a door.
The firefighter applies force 18 inches from the fulcrum point at the door frame.
What simple machine principle does this demonstrate?