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Mechanical Comprehension

Which of the following is not true of a first-class lever?

decreases distance

A first-class lever is used to increase force or distance while changing the direction of the force. The lever pivots on a fulcrum and, when a force is applied to the lever at one side of the fulcrum, the other end moves in the opposite direction. The position of the fulcrum also defines the mechanical advantage of the lever. If the fulcrum is closer to the force being applied, the load can be moved a greater distance at the expense of requiring a greater input force. If the fulcrum is closer to the load, less force is required but the force must be applied over a longer distance. An example of a first-class lever is a seesaw / teeter-totter.

Shop Information

A __________ is driven by a motor and used to shape and form edge contours.

router

A router is a tool that a worker uses to rout (hollow out), shape, or contour an area in relatively hard material like wood or plastic.

Mechanical Comprehension

The advantage of using a third-class lever is that it increases:

the speed of the load

A third-class lever is used to increase distance traveled by an object in the same direction as the force applied. The fulcrum is at one end of the lever, the object at the other, and the force is applied between them. This lever does not impart a mechanical advantage as the effort force must be greater than the load but does impart extra speed to the load. Examples of third-class levers are shovels and tweezers.

Word Knowledge

Proximity most nearly means:

nearness

Closeness.

Mechanical Comprehension

A block and tackle with four pulleys would have a mechanical advantage of:

Two or more pulleys used together constitute a block and tackle which, unlike a fixed pulley, does impart mechanical advantage as a function of the number of pulleys that make up the arrangement. So, for example, a block and tackle with three pulleys would have a mechanical advantage of three.

Math Knowledge

The endpoints of this line segment are at (-2, 2) and (2, -6). What is the slope-intercept equation for this line?

y = -2x - 2

The slope-intercept equation for a line is y = mx + b where m is the slope and b is the y-intercept of the line. From the graph, you can see that the y-intercept (the y-value from the point where the line crosses the y-axis) is -2. The slope of this line is the change in y divided by the change in x. The endpoints of this line segment are at (-2, 2) and (2, -6) so the slope becomes:

m = \( \frac{\Delta y}{\Delta x} \) = \( \frac{(-6.0) - (2.0)}{(2) - (-2)} \) = \( \frac{-8}{4} \)
m = -2

Plugging these values into the slope-intercept equation:

y = -2x - 2

Electronics Information

What is the frequency of most household electrical systems?

60Hz

Electricity is delivered from power stations to customers as AC because it provides a more efficient way to transport electricity over long distances. Most households use electricity with a frequency of 60Hz.

Mechanical Comprehension

If you lift a 30 lbs. rock 24 ft. from the ground, how much work have you done?

720 ft⋅lb

Work is force times distance. In this case, the force is the weight of the rock so:
\( W = F \times d \)
\( W = 30 \times 24 \)
\( W = 720 \)

Word Knowledge

Clarity most nearly means:

lucidity

Clearness.

Electronics Information

Why is an insulator a poor conductor of electricity?

an insulator has few free electrons

Insulators have valence shells that are more than half full of electrons and, as such, are tightly bound to the nucleus and difficult to move from one atom to another.