ASVAB Mechanical Comprehension Practice Test 866017 Results

	Your Results	Global Average
Questions	5	5
Correct	0	2.94
Score	0%	59%

Review

1 If the force applied at the blue arrow over 6 ft. moves the green box 2.0 ft., what is the mechanical advantage of this lever?

55% Answer Correctly

	3
	3.3
	2.7
	-4

Solution

Mechanical advantage (MA) can be calculated knowing only the distance the effort (blue arrow) moves and the distance the resistance (green box) moves. The equation is:

MA = \( \frac{E_d}{R_d} \)

where E_d is the effort distance and R_d is the resistance distance. For this problem, the equation becomes:

MA = \( \frac{6 ft.}{2.0 ft.} \) = 3

You might be wondering how having an effort distance of 3 times the resistance distance is an advantage. Remember the principle of moments. For a lever in equilibrium the effort torque equals the resistance torque. Because torque is force x distance, if the effort distance is 3 times the resistance distance, the effort force must be \( \frac{1}{3} \) the resistance force. You're trading moving 3 times the distance for only having to use \( \frac{1}{3} \) the force.

2 What is the efficiency of a machine has work input of 185 ft⋅lb and work output of 74 ft⋅lb?

67% Answer Correctly

	40%
	60%
	80%
	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:
\( Efficiency = \frac{Work_{out}}{Work_{in}} \times 100 \) \( = \frac{74 ft⋅lb}{185 ft⋅lb} \times 100 \) \( = 40% \) %

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

50% Answer Correctly

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

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.

What type of load is sudden and for a relatively short duration?

69% Answer Correctly

	dynamic load
	impact load
	concentrated load
	non-uniformly distributed load

Solution

A concentrated load acts on a relatively small area of a structure, a static uniformly distributed load doesn't create specific stress points or vary with time, a dynamic load varies with time or affects a structure that experiences a high degree of movement, an impact load is sudden and for a relatively short duration and a non-uniformly distributed load creates different stresses at different locations on a structure.

The principle of moments defines equilibrium in terms of:

53% Answer Correctly

	speed
	torque
	energy
	power

Solution

According to the principle of moments, you can maintain equilibrium if the moments (forces) tending to clockwise rotation are equal to the moments tending to counterclockwise rotation. Another name for these moments of force is torque.