NFST Mechanical Aptitude 4 — Questions and Answers
Question 1: Which simple machine is a wedge most similar to in terms of mechanical principle?
- A pulley
- An inclined plane (Correct answer)
- A wheel and axle
- A lever
Correct answer: An inclined plane
A wedge is essentially a moving inclined plane; both convert a smaller input force applied over a longer distance into a larger output force over a shorter distance.
Question 2: A fire pump discharges water at 150 PSI. If a nozzle is opened on a hoseline 100 feet above the pump, approximately how much pressure is lost to elevation?
- 22 PSI
- 43 PSI (Correct answer)
- 65 PSI
- 100 PSI
Correct answer: 43 PSI
Water loses approximately 0.434 PSI per foot of elevation: 100 ft × 0.434 ≈ 43 PSI.
Question 3: An electric motor drives a pump through a belt and pulley system. The motor pulley is 4 inches in diameter and the pump pulley is 8 inches in diameter. If the motor runs at 1800 RPM, what is the pump speed?
- 450 RPM
- 900 RPM (Correct answer)
- 1800 RPM
- 3600 RPM
Correct answer: 900 RPM
Pump speed = Motor RPM × (Motor pulley diameter / Pump pulley diameter) = 1800 × (4/8) = 900 RPM.
Question 4: What does it mean when a mechanical system has a mechanical advantage of less than 1?
- The system multiplies force but reduces distance
- The system multiplies distance but requires more input force (Correct answer)
- The system is broken and non-functional
- The system operates with zero friction
Correct answer: The system multiplies distance but requires more input force
A mechanical advantage less than 1 means the output force is smaller than the input force, but the output moves a greater distance (trading force for speed or distance).
Question 5: Which type of valve is best suited for fully open or fully closed service and is NOT designed for throttling flow?
- Globe valve
- Needle valve
- Gate valve (Correct answer)
- Ball valve with regulator
Correct answer: Gate valve
Gate valves are designed only for full-open or full-closed positions; using them for throttling causes vibration and accelerated wear.
Question 6: In a hydraulic system, a small piston with an area of 2 sq in has 50 lbs of force applied to it. What force is exerted by a large piston with an area of 20 sq in?
- 5 lbs
- 50 lbs
- 250 lbs
- 500 lbs (Correct answer)
Correct answer: 500 lbs
Pascal's Law: pressure is equal throughout the fluid; Pressure = 50/2 = 25 PSI; Force on large piston = 25 × 20 = 500 lbs.
Question 7: A firefighter carries a 60-lb hose bundle and climbs a ladder at a rate of 2 feet per second. How much power is required (in ft-lbs/sec)?
- 30 ft-lbs/sec
- 60 ft-lbs/sec
- 120 ft-lbs/sec (Correct answer)
- 180 ft-lbs/sec
Correct answer: 120 ft-lbs/sec
Power = Force × Velocity = 60 lbs × 2 ft/sec = 120 ft-lbs/sec.
NFST Mechanical Aptitude 4
Which simple machine is a wedge most similar to in terms of mechanical principle?