EEI Tech Mechanical Concept Flashcards

Two gears mesh together. The driver gear has 10 teeth and the driven gear has 30 teeth. If the driver turns at 300 RPM, how fast does the driven gear turn?

Answer: 100 RPM

Speed is inversely proportional to teeth count: 300 × (10/30) = 100 RPM.

A lever has its fulcrum at the center, with equal arm lengths. To lift a 50 lb load, how much effort force is needed at the other end?

Answer: 50 lb

With equal arm lengths the mechanical advantage is 1, so effort equals load.

When two pulleys are connected by a belt, what determines the direction the driven pulley turns relative to the driver in an open belt drive?

Answer: Same direction

An open (uncrossed) belt drive makes both pulleys turn in the same direction.

A hydraulic system applies 20 lb of force on a small piston of 1 sq in. The large piston has 5 sq in area. What output force is produced?

Answer: 100 lb

Pressure is equal, so force scales with area: 20 × (5/1) = 100 lb.

Which simple machine is a doorknob an example of?

Answer: Wheel and axle

A doorknob turns a small axle using a larger wheel, a classic wheel and axle.

If a spring stretches 2 inches under a 10 lb load, how far will it stretch under a 25 lb load (assuming it stays within its elastic limit)?

Answer: 5 inches

By Hooke's law extension is proportional to force: 2 × (25/10) = 5 inches.

Which type of friction must be overcome first to start a stationary object moving?

Answer: Static friction

Static friction holds objects at rest and is generally greater than kinetic friction.