Applying Mechanical Reasoning Flashcards

A water pipe narrows from a 4-inch diameter to a 2-inch diameter. How does the water velocity change at the narrow section?

Answer: Velocity quadruples

Area decreases by a factor of 4 (since area ∝ radius²), so velocity must increase by 4 to maintain constant flow rate.

A spring with a spring constant of 50 lb/in is compressed 3 inches. How much force is required to hold it compressed?

Answer: 150 lb

Using Hooke's Law: F = k × x = 50 lb/in × 3 in = 150 lb.

A bolt is being tightened using a torque wrench set to 60 ft-lb. If the wrench handle is 2 feet long, what perpendicular force must be applied?

Answer: 30 lb

Force = Torque ÷ Distance = 60 ft-lb ÷ 2 ft = 30 lb.

Which material would be BEST for a machine part that must absorb repeated impact without cracking?

Answer: Ductile low-carbon steel

Ductile low-carbon steel has high toughness and absorbs impact energy by deforming rather than fracturing.

A pneumatic cylinder has a bore diameter of 4 inches and is supplied with air at 100 PSI. Approximately what force can it generate?

Answer: 1,257 lb

Force = Pressure × Area = 100 PSI × π(2²) ≈ 100 × 12.57 ≈ 1,257 lb.

When a metal shaft is rotated by a belt drive, the belt on the slack side has 50 lb of tension and the tight side has 200 lb. What net force drives the pulley?

Answer: 150 lb

Net driving force = tight side tension − slack side tension = 200 − 50 = 150 lb.

Two objects are connected by a rope over a frictionless pulley. Object A weighs 80 lb and Object B weighs 50 lb. What is the acceleration direction of the system?

Answer: Object A accelerates downward

The heavier object (A at 80 lb) accelerates downward because the net unbalanced force acts in that direction.