ASVAB Mechanical Comprehension Practice Test 614167 Results

	Your Results	Global Average
Questions	5	5
Correct	0	3.40
Score	0%	68%

Review

1 What is the efficiency of a machine has work input of 210 ft⋅lb and work output of 199 ft⋅lb?

67% Answer Correctly

	5%
	47%
	95%
	0%

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:
\( Efficiency = \frac{Work_{out}}{Work_{in}} \times 100 \) \( = \frac{199 ft⋅lb}{210 ft⋅lb} \times 100 \) \( = 95% \) %

2 How much work can a 4 hp engine do in 3 seconds?

52% Answer Correctly

	16 ft⋅lb
	0 ft⋅lb
	6600 ft⋅lb
	8 ft⋅lb

Solution

Horsepower (hp) is a common measure of power output for complex machines. By definition, a 1 hp machine does 550 ft⋅lb of work in 1 second: 1 hp = 550 ft⋅lb/s. Substituting the variables for this problem gives us:
\( W = 4 hp \times 550 \frac{ft⋅lb}{s} \times 3s = 6600 ft⋅lb \)

A screw is most like which of the following other simple machines?

50% Answer Correctly

	inclined plane
	wheel and axle
	first-class lever
	block and tackle

Solution

A screw is an inclined plane wrapped in ridges (threads) around a cylinder. The distance between these ridges defines the pitch of the screw and this distance is how far the screw advances when it is turned once. The mechanical advantage of a screw is its circumference divided by the pitch.

Friction resists movement in a direction __________ to the movement.

81% Answer Correctly

	perpendicular
	opposite
	normal
	parallel

Solution

Friction resists movement. Kinetic (also called sliding or dynamic) friction resists movement in a direction opposite to the movement. Because it opposes movement, kinetic friction will eventually bring an object to a stop. An example is a rock that's sliding across ice.

The steering wheel of a car is an example of which type of simple machine?

89% Answer Correctly

	first-class lever
	wheel and axle
	block and tackle
	fixed pulley

Solution

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.