Applying Mechanical Reasoning Flashcards

A lever is 10 feet long with the fulcrum placed 2 feet from the load end. To lift a 200-lb load, approximately how much force must be applied at the other end?

Answer: 50 lb

With an 8-foot effort arm and 2-foot load arm, mechanical advantage is 4, so 200 ÷ 4 = 50 lb of force needed.

Two gears mesh together. Gear A has 40 teeth and Gear B has 10 teeth. If Gear A rotates at 100 RPM, how fast does Gear B rotate?

Answer: 400 RPM

Gear ratio = 40/10 = 4, so Gear B rotates 4 times faster: 100 × 4 = 400 RPM.

A block and tackle system has 4 rope segments supporting the load. If the load weighs 400 lb, how much pulling force is required (ignoring friction)?

Answer: 100 lb

With 4 supporting rope segments, the mechanical advantage is 4, so 400 ÷ 4 = 100 lb of force is needed.

A hydraulic press has an input piston with area 2 sq in and an output piston with area 20 sq in. If 50 lb of force is applied to the input, what force does the output exert?

Answer: 500 lb

Hydraulic mechanical advantage = output area ÷ input area = 20/2 = 10, so output force = 50 × 10 = 500 lb.

A wedge is being driven into a log. What happens to the mechanical advantage if the wedge angle is made smaller (thinner wedge)?

Answer: Mechanical advantage increases

A thinner wedge has a smaller angle, which increases mechanical advantage, making it easier to split the wood with less force.

A screw has 20 threads per inch and a handle radius of 6 inches. What is its mechanical advantage?

Answer: About 754

MA = 2π × handle radius × threads per inch = 2π × 6 × 20 ≈ 754.

Which type of lever has the effort applied between the fulcrum and the load?

Answer: Third-class lever

A third-class lever has effort between the fulcrum and load, trading mechanical advantage for speed and range of motion.