Mechanical Comprehension Flashcards

A hydraulic jack uses a small piston with area 2 sq in and a large piston with area 20 sq in. If you apply 50 lbs to the small piston, what force does the large piston exert?

Answer: 500 lbs

Pascal's law: force scales with area ratio, so 50 × (20/2) = 500 lbs.

Which type of gear arrangement reverses the direction of rotation between the input and output shaft?

Answer: Two meshing spur gears

Two meshing spur gears always rotate in opposite directions.

A spring with a spring constant of 200 N/m is compressed 0.05 m. How much potential energy is stored?

Answer: 0.25 J

Spring potential energy = ½kx² = ½ × 200 × 0.05² = 0.25 J.

A solid steel cylinder and a hollow steel cylinder of the same outer diameter and length are both rolled down an incline. Which reaches the bottom first?

Answer: The solid cylinder

The solid cylinder has a lower moment of inertia relative to its mass, so it accelerates faster down the incline.

What is the mechanical advantage of a single fixed pulley?

Answer: 1

A single fixed pulley only changes the direction of force and provides a mechanical advantage of 1.

Water flows through a pipe that narrows from 4 inches in diameter to 2 inches in diameter. How does the water speed change?

Answer: It quadruples

By the continuity equation, halving the diameter reduces area by factor 4, so speed increases 4×.

A torque wrench applies 30 ft-lbs of torque using a 1.5 ft handle. What force must be applied?

Answer: 20 lbs

Torque = Force × Distance, so Force = 30 / 1.5 = 20 lbs.

A cam converts which type of motion into another?

Answer: Rotary to oscillating/linear

A cam converts rotary motion into reciprocating or oscillating linear motion via a follower.

Two objects of different masses are dropped from the same height in a vacuum. Which hits the ground first?

Answer: They hit at the same time

In a vacuum, gravity accelerates all objects equally regardless of mass, so both hit simultaneously.

Which material is the best conductor of heat?

Answer: Copper

Copper has a very high thermal conductivity, making it the best heat conductor among these options.

A driver gear with 40 teeth meshes with a driven gear with 10 teeth. If the driver turns at 100 RPM, what is the speed of the driven gear?

Answer: 400 RPM

Speed ratio is inverse of tooth ratio: 100 × (40/10) = 400 RPM.

Which class of lever has the fulcrum located between the effort and the load?

Answer: First class

A first-class lever (like a seesaw or crowbar) has the fulcrum between effort and load.

A belt connecting two pulleys slips when the tension difference between tight and slack sides is too great. What is the most effective fix?

Answer: Increase belt tension

Increasing belt tension raises friction force, allowing greater torque transfer without slipping.

An object moving in a circle at constant speed has which type of acceleration?

Answer: Centripetal acceleration directed inward

Centripetal acceleration is always directed toward the center of the circle, causing the direction change.

A screw has 20 threads per inch. How far does it advance per complete revolution?

Answer: 0.05 inches

Advance per revolution = 1 ÷ threads per inch = 1 ÷ 20 = 0.05 inches.

Which simple machine is essentially an inclined plane wrapped around a cylinder?

Answer: Screw

A screw is an inclined plane (ramp) wound helically around a cylindrical shaft.

If a 10 kg box is pushed across a floor with a coefficient of kinetic friction of 0.3, what is the friction force? (g = 10 m/s²)

Answer: 30 N

Friction force = μ × N = 0.3 × (10 × 10) = 30 N.

In a compound pulley system with 4 rope segments supporting the load, what is the mechanical advantage?

Answer: 4

Mechanical advantage of a pulley system equals the number of rope segments supporting the load.

Which valve type is best suited for fully open or fully closed flow control, not for throttling?

Answer: Gate valve

Gate valves are designed for on/off service and should not be used for throttling as the gate can vibrate and erode.

A steel beam deflects more when a load is applied at its center than at its end because:

Answer: The bending moment is greatest at the center

A center load on a simply supported beam creates maximum bending moment at midspan, causing greatest deflection there.