ASVAB Mechanical Comprehension Practice Test 347726 Results

	Your Results	Global Average
Questions	5	5
Correct	0	3.20
Score	0%	64%

Review

The mechanical advantage of connected gears is proportional to which characteristic of the gears?

73% Answer Correctly

	diameter
	number of teeth
	circumference
	speed

Solution

The mechanical advantage (amount of change in speed or torque) of connected gears is proportional to the number of teeth each gear has. Called gear ratio, it's the ratio of the number of teeth on the larger gear to the number of teeth on the smaller gear. For example, a gear with 12 teeth connected to a gear with 9 teeth would have a gear ratio of 4:3.

2 What is the efficiency of a machine has work input of 195 ft⋅lb and work output of 117 ft⋅lb?

68% Answer Correctly

	30%
	40%
	60%
	120%

Solution

Due to friction, a machine will never be able to utilize 100% of its work input. A certain percentage of that input will be lost in overcoming friction within the machine. Effeciency is a measure of how much of a machine's work input can be turned into useful work output and is calculated by dividing work output by work input and multiplying the result by 100:
\( Efficiency = \frac{Work_{out}}{Work_{in}} \times 100 \) \( = \frac{117 ft⋅lb}{195 ft⋅lb} \times 100 \) \( = 60% \) %

Which of the following is the formula for torque?

62% Answer Correctly

	τ = rF
	τ = F/r²
	τ = F/r
	τ = r/F

Solution

Torque measures force applied during rotation: τ = rF. Torque (τ, the Greek letter tau) = the radius of the lever arm (r) multiplied by the force (F) applied. Radius is measured from the center of rotation or fulcrum to the point at which the perpendicular force is being applied. The resulting unit for torque is newton-meter (N-m) or foot-pound (ft-lb).

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

51% Answer Correctly

	increases distance
	decreases distance
	increases force
	changes the direction of force

Solution

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.

According to Boyle's law, for a fixed amount of gas kept at a fixed temperature, which of the following are inversely proportional?

64% Answer Correctly

	volume, mass
	density, volume
	pressure, density
	pressure, volume

Solution

Boyle's law states that "for a fixed amount of an ideal gas kept at a fixed temperature, pressure and volume are inversely proportional".