ASVAB Mechanical Comprehension Practice Test 869639 Results

	Your Results	Global Average
Questions	5	5
Correct	0	3.01
Score	0%	60%

Review

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

50% Answer Correctly

	inclined plane
	block and tackle
	wheel and axle
	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.

2 If the force applied at the blue arrow over 8 ft. moves the green box 1.14 ft., what is the mechanical advantage of this lever?

56% Answer Correctly

	10.5
	16
	21
	7

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 = \( \frac{8 ft.}{1.14 ft.} \) = 7

You might be wondering how having an effort distance of 7 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 7 times the resistance distance, the effort force must be \( \frac{1}{7} \) the resistance force. You're trading moving 7 times the distance for only having to use \( \frac{1}{7} \) the force.

The mass of an object correlates to the size of the object but ultimately depends on:

66% Answer Correctly

	the object's potential energy
	gravity
	the object's density
	the object's weight

Solution

Mass is a measure of the amount of matter in an object. In general, larger objects have larger mass than smaller objects but mass ultimately depends on how compact (dense) a substance is.

Which class of lever is used to increase force on an object in the same direction as the force is applied?

53% Answer Correctly

	first
	all of these
	third
	second

Solution

A second-class lever is used to increase force on an object in the same direction as the force is applied. This lever requires a smaller force to lift a larger load but the force must be applied over a greater distance. The fulcrum is placed at one end of the lever and mechanical advantage increases as the object being lifted is moved closer to the fulcrum or the length of the lever is increased. An example of a second-class lever is a wheelbarrow.

Hydraulics is the transmission of force through the use of which of the following?

73% Answer Correctly

	torque
	liquids
	gear systems
	air pressure

Solution

Hydraulics is the transmission of force through the use of liquids. Liquids are especially suited for transferring force in complex machines because they compress very little and can occupy very small spaces. Hydraulic pressure is calculated by dividing force by the area over which it is applied: P = F/A where F is force in pounds, A is area in square inches, and the resulting pressure is in pounds per square inch (psi).