ASVAB Mechanical Comprehension Practice Test 421614 Results

	Your Results	Global Average
Questions	5	5
Correct	0	2.72
Score	0%	54%

Review

A box is resting on a smooth floor. Static friction is present:

59% Answer Correctly

	only if normal force is present
	when an attempt is made to move the box
	if the coefficient of friction is greater than one
	at all times

Solution

For any given surface, the coefficient of static friction is higher than the coefficient of kinetic friction. More force is required to initally get an object moving than is required to keep it moving. Additionally, static friction only arises in response to an attempt to move an object (overcome the normal force between it and the surface).

Which of the following is not a type of structural load?

50% Answer Correctly

	dead load
	occupancy load
	live load
	wind load

Solution

Dead load is the weight of the building and materials, live load is additional weight due to occupancy or use, snow load is the weight of accumulated snow on a structure and wind load is the force of wind pressures against structure surfaces.

What is work?

60% Answer Correctly

	Force per unit time
	The potential for exertion
	Force per unit distance
	The movement of an object by a force

Solution

Work is accomplished when force is applied to an object: W = Fd where F is force in newtons (N) and d is distance in meters (m). Thus, the more force that must be applied to move an object, the more work is done and the farther an object is moved by exerting force, the more work is done. By definition, work is the displacement of an object resulting from applied force.

Which of the following is not a modulus of elasticity?

47% Answer Correctly

	bulk modulus
	stress modulus
	shear modulus
	stretch modulus

Solution

The modulus of elasticity measures how much a material or structure will deflect under stress. Stretch modulus is longitudinal stretch (like stretching raw bread dough), shear modulus is longitudinal deflection (like the horizontal displacement of a stack of magzines when a heavy object is placed upon them), and bulk modulus is compression of volume (like the compression of a loaf of bread under a heavy can at the bottom of a grocery bag).

5 If the force applied at the blue arrow over 7 ft. moves the green box 1.75 ft., what is the mechanical advantage of this lever?

55% Answer Correctly

	12
	4
	3.6
	5

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 = \( \frac{7 ft.}{1.75 ft.} \) = 4

You might be wondering how having an effort distance of 4 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 4 times the resistance distance, the effort force must be \( \frac{1}{4} \) the resistance force. You're trading moving 4 times the distance for only having to use \( \frac{1}{4} \) the force.