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Mechanical Comprehension

Which of the following represents how much two materials resist sliding across each other?

coefficient of friction

Coefficient of friction (μ) represents how much two materials resist sliding across each other. Smooth surfaces like ice have low coefficients of friction while rough surfaces like concrete have high μ.

Math Knowledge

What is 7a³ + 7a³?

14a³

To combine like terms, add or subtract the coefficients (the numbers that come before the variables) of terms that have the same variable raised to the same exponent.

7a³ + 7a³ = 14a³

General Science

The gravitational interaction of Earth and the Moon is responsible for which of these?

tides

Tides are caused by the gravitational interaction of Earth and the Moon.

Electronics Information

What kind of diode allows current to flow in the opposite direction once a certain voltage threshold is reached?

zener diode

A diode allows current to pass easily in one direction and blocks current in the other direction. A zener diode is a diode which allows current to flow in one direction as normal and will also allow current flow in the reverse direction when the voltage is above a certain value. This value is called the breakdown voltage.

Mechanical Comprehension

The mechanical advantage of a wheel and axle is equal to the:

ratio of the diameters of the wheels

A wheel and axle uses two different diameter wheels mounted to a connecting axle. Force is applied to the larger wheel and large movements of this wheel result in small movements in the smaller wheel. Because a larger movement distance is being translated to a smaller distance, force is increased with a mechanical advantage equal to the ratio of the diameters of the wheels. An example of a wheel and axle is the steering wheel of a car.

Word Knowledge

The sweet cookie was a perfect foil to the sour lemon sorbet.

complement

One that enhances or underscores by contrast.

Mechanical Comprehension

If this lever is in equilibrium with an effort force of 10.0 ft. lb. at the blue arrow and a resistance force of 3 ft. lb. at the green box, what is its mechanical advantage?

0.3

Mechanical advantage (MA) is the ratio by which effort force relates to resistance force. If both forces are known, calculating MA is simply a matter of dividing resistance force by effort force:

MA = \( \frac{F_r}{F_e} \) = \( \frac{3 ft.}{10.0 ft.} \) = 0.3

In this case, the mechanical advantage is less than one meaning that each unit of effort force results in just 0.3 units of resistance force. However, a third class lever like this isn't designed to multiply force like a first class lever. A third class lever is designed to multiply distance and speed at the resistance by sacrificing force at the resistance. Different lever styles have different purposes and multiply forces in different ways.

General Science

Which of the following would be used in eye glasses to correct nearsightedness?

concave lens

Unlike curved mirrors that operate on the principle of reflection, lenses utilize refraction. A convex lens is thicker in the middle than on the edges and converges light while a concave lens is thicker on the edges than in the middle and diffuses light. A common use for curved lenses is in eye glasses where a convex lens is used to correct farsightedness and a concave lens is used to correct nearsightedness.

General Science

Antigens are found on the outside of which blood cells?

red

Blood is categorized into four different types (A, B, AB, and O) based on the type of antigens found on the outside of the red blood cells. Additionally, each type can be negative or positive based on whether or not the cells have an antigen called the Rh factor.

Mechanical Comprehension

70 lbs. of effort is used by a machine to lift a 350 lbs. box. What is the mechanical advantage of the machine?

Mechanical advantage is resistance force divided by effort force:

MA = \( \frac{F_r}{F_e} \) = \( \frac{350 lbs.}{70 lbs.} \) = 5