ASVAB Mechanical Comprehension Practice Test 479737 Results

	Your Results	Global Average
Questions	5	5
Correct	0	3.22
Score	0%	64%

Review

1 If input effort is 300 ft⋅lb, what output effort will be produced by a machine with a mechanical advantage of 4?

79% Answer Correctly

	0ft⋅lb
	600ft⋅lb
	1200 ft⋅lb
	2400ft⋅lb

Solution

Mechanical advantage is the ratio of output force to input force and tells us by how many times a machine multiplies input effort. So, a machine with a mechanical advantage of 4 will multiply an input effort of 300 ft⋅lb by 4 to produce an output effort of 1200 ft⋅lb.

Which class of lever offers no mechanical advantage?

45% Answer Correctly

	second
	third
	first
	none of these, all levers offer mechanical advantage

Solution

A third-class lever is used to increase distance traveled by an object in the same direction as the force applied. The fulcrum is at one end of the lever, the object at the other, and the force is applied between them. This lever does not impart a mechanical advantage as the effort force must be greater than the load but does impart extra speed to the load. Examples of third-class levers are shovels and tweezers.

3 If the force applied at the blue arrow over 9 ft. moves the green box 1.5 ft., what is the mechanical advantage of this lever?

55% Answer Correctly

	13
	6.6
	6
	5.4

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 = \( \frac{9 ft.}{1.5 ft.} \) = 6

You might be wondering how having an effort distance of 6 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 6 times the resistance distance, the effort force must be \( \frac{1}{6} \) the resistance force. You're trading moving 6 times the distance for only having to use \( \frac{1}{6} \) the force.

Which of the following is the formula for hydraulic pressure?

58% Answer Correctly

	P = F/A
	P = F/A²
	P = FA²
	P = FA

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).

Friction resists movement in a direction __________ to the movement.

82% Answer Correctly

	normal
	parallel
	opposite
	perpendicular

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.