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Electronics Information

The watt is a unit of measurement for:

power

Electrical power is measured in watts (W) and is calculated by multiplying the voltage (V) applied to a circuit by the resulting current (I) that flows in the circuit: P = IV. In addition to measuring production capacity, power also measures the rate of energy consumption and many loads are rated for their consumption capacity. For example, a 60W lightbulb utilizes 60W of energy to produce the equivalent of 60W of heat and light energy.

Word Knowledge

Stealth most nearly means:

furtiveness

The act of moving secretly or unnoticed.

Mechanical Comprehension

A watt is the unit for which of the following?

power

Power is the rate at which work is done, P = w/t, or work per unit time. The watt (W) is the unit for power and is equal to 1 joule (or newton-meter) per second. Horsepower (hp) is another familiar unit of power used primarily for rating internal combustion engines. 1 hp equals 746 watts.

Automotive Information

Which of the following is not an advantage that disc brakes have over drum brakes?

use less brake fluid

Brakes utlize friction to slow vehicle tires. Drum brakes employ a cast iron drum that roates with the vehicle axle. When hydraulic pressure is applied to the brake assemblies at the wheels, internal pistons expand and push brake shoes outward into contact with the brake drum slowing the rotation of the axle. More powerful disc brakes operate by pinching a rotating disc betweeen two brake pads and allow for a larger surface area to contact the disc, provide more force, and are more easily cooled.

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

Mandate most nearly means:

command

An official order or commission to do something.

Mechanical Comprehension

If the green box weighs 30 lbs. and is 8 ft. from the fulcrum, how much force would need to be applied at the blue arrow to balance the lever if the arrow's distance from the fulcrum is 9 ft.?

26.67 lbs.

To balance this lever the torques at the green box and the blue arrow must be equal. Torque is weight x distance from the fulcrum so the equation for equilibrium is:

R_ad_a = R_bd_b

where a represents the green box and b the blue arrow, R is resistance (weight/force) and d is the distance from the fulcrum.

Solving for R_b, our missing value, and plugging in our variables yields:

R_b = \( \frac{R_ad_a}{d_b} \) = \( \frac{30 lbs. \times 8 ft.}{9 ft.} \) = \( \frac{240 ft⋅lb}{9 ft.} \) = 26.67 lbs.

Automotive Information

Which of the following is the correct order for the engine stroke cycle?

intake, compression, power, exhaust

The stroke cycle order is intake stroke, compression stroke, power stroke, exhaust stroke.

General Science

Secondary consumers that also eat producers are known as:

omnivores

Secondary consumers (carnivores) subsist mainly on primary consumers. Omnivores are secondary consumers that also eat producers. Examples are rats, fish, and chickens.

Mechanical Comprehension

Which of the following statements about this pulley configuration is false?

Only multiplies the effort force

A block and tackle is a combination of one or more fixed pulleys and one or more movable pulleys where the fixed pulleys change the direction of the effort force and the movable pulleys multiply it. The mechanical advantage is equal to the number of times the effort force changes direction and can be increased by adding more pulley wheels to the system. An easy way to find the mechanical advantage of a block and tackle pulley system is to count the number of ropes that support the resistance.