Mechanical Reasoning Principles Flashcards

A block-and-tackle system uses 4 rope segments supporting a load. Ignoring friction, how much force is needed to lift a 200 lb load?

Answer: 50 lb

With 4 supporting rope segments the mechanical advantage is 4, so the required force is 200 ÷ 4 = 50 lb.

Two gears mesh together. Gear A has 12 teeth and Gear B has 36 teeth. If Gear A rotates at 900 RPM, how fast does Gear B rotate?

Answer: 300 RPM

Gear ratio = 12/36 = 1/3, so Gear B spins at 900 × (1/3) = 300 RPM.

A lever is 10 ft long with the fulcrum 2 ft from the load end. A 500 lb load sits at the load end. How much effort is required at the other end?

Answer: 125 lb

Effort arm = 8 ft, load arm = 2 ft; effort = 500 × (2/8) = 125 lb.

Which type of wrench provides the greatest mechanical advantage when loosening a very tight bolt?

Answer: Breaker bar with long handle

A longer handle increases the torque (force × distance), giving the breaker bar the greatest mechanical advantage.

Water flows through a pipe that narrows from 6-inch diameter to 3-inch diameter. What happens to the water's velocity in the narrow section?

Answer: It quadruples

Cross-sectional area decreases by a factor of 4 (diameter halved), so by continuity the velocity must quadruple.

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

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

On an inclined plane, which factor does NOT affect the mechanical advantage gained when sliding a heavy object up the ramp?

Answer: Weight of the object

Mechanical advantage of an inclined plane = ramp length ÷ ramp height; the object's weight affects the required force but not the MA itself.