ASVAB Mechanical Comprehension Practice Test 262492 Results

	Your Results	Global Average
Questions	5	5
Correct	0	3.34
Score	0%	67%

Review

What defines the mechanical advantage of a first class lever?

65% Answer Correctly

	input force
	position of the fulcrum
	output force
	output distance

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.

For a hydraulic system, pressure applied to the input of the system will increase the pressure in which parts of the system?

58% Answer Correctly

	the portions of the system at an altitude above the input
	the portions of the system at an altitude below the input
	everywhere in the system
	all of these are correct

Solution

Pascal's law states that a pressure change occurring anywhere in a confined incompressible fluid is transmitted throughout the fluid such that the same change occurs everywhere. For a hydraulic system, this means that a pressure applied to the input of the system will increase the pressure everywhere in the system.

3 If you lift a 18 lbs. rock 39 ft. from the ground, how much work have you done?

70% Answer Correctly

	1404 ft⋅lb
	702 ft⋅lb
	57 ft⋅lb
	0 ft⋅lb

Solution

Work is force times distance. In this case, the force is the weight of the rock so:
\( W = F \times d \)
\( W = 18 \times 39 \)
\( W = 702 \)

Friction resists movement in a direction __________ to the movement.

81% Answer Correctly

	normal
	perpendicular
	opposite
	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.

5 If the force applied at the blue arrow over 3 ft. moves the green box 0.33 ft., what is the mechanical advantage of this lever?

56% Answer Correctly

	9
	18
	13.5
	9.9

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 = \( \frac{3 ft.}{0.33 ft.} \) = 9

You might be wondering how having an effort distance of 9 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 9 times the resistance distance, the effort force must be \( \frac{1}{9} \) the resistance force. You're trading moving 9 times the distance for only having to use \( \frac{1}{9} \) the force.