Applying Mechanical Reasoning Flashcards

A steel I-beam is used rather than a solid rectangular beam of the same weight. What is the main advantage of the I-beam shape?

Answer: It resists bending more efficiently by placing material where stress is highest

The I-beam shape concentrates material in the flanges where bending stress is greatest, maximizing stiffness per unit weight.

A valve is described as 'normally closed.' What does this mean in a pneumatic circuit?

Answer: No air flows through the valve until an actuating signal opens it

A normally closed (NC) valve blocks flow in its default rest state and only allows flow when an actuating signal is applied.

A rotating shaft develops a crack perpendicular to its axis. What type of stress is most likely causing this failure?

Answer: Bending fatigue stress

Cracks perpendicular to the shaft axis on a rotating shaft are characteristic of cyclic bending fatigue, which creates tension-compression cycles.

Heat is transferred through a metal rod from a hot end to a cool end. What mode of heat transfer is this?

Answer: Conduction

Heat traveling through a solid material from molecule to molecule is conduction — the dominant heat transfer mode in metals.

A pump raises water 40 feet and delivers 100 gallons per minute. One gallon of water weighs about 8.34 lb. Approximately how much horsepower is required (1 HP = 33,000 ft-lb/min)?

Answer: 1 HP

Power = (100 gal/min × 8.34 lb/gal × 40 ft) ÷ 33,000 = 33,360 ÷ 33,000 ≈ 1 HP.

A nut is seized on a bolt. A mechanic applies penetrating oil and waits, then uses a longer breaker bar. The longer bar helps because it:

Answer: Increases the torque applied with the same force

A longer bar increases the lever arm distance, so the same applied force produces greater torque (Torque = Force × Distance).

A differential gear system in a vehicle allows the two drive wheels to rotate at different speeds. When is this most important?

Answer: When turning a corner

During cornering, the outer wheel must travel a longer arc than the inner wheel, requiring different rotational speeds — the differential allows this.