Mechanical Aptitude Flashcards

Which simple machine is a wedge most similar to in terms of mechanical principle?

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.

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?

Answer: 43 PSI

Water loses approximately 0.434 PSI per foot of elevation: 100 ft × 0.434 ≈ 43 PSI.

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?

Answer: 900 RPM

Pump speed = Motor RPM × (Motor pulley diameter / Pump pulley diameter) = 1800 × (4/8) = 900 RPM.

What does it mean when a mechanical system has a mechanical advantage of less than 1?

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).

Which type of valve is best suited for fully open or fully closed service and is NOT designed for throttling flow?

Answer: Gate valve

Gate valves are designed only for full-open or full-closed positions; using them for throttling causes vibration and accelerated wear.

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?

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.

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)?

Answer: 120 ft-lbs/sec

Power = Force × Velocity = 60 lbs × 2 ft/sec = 120 ft-lbs/sec.