ASVAB Mechanical Comprehension Practice Test 452539 Results

	Your Results	Global Average
Questions	5	5
Correct	0	3.39
Score	0%	68%

Review

Concurrent forces:

55% Answer Correctly

	act along the same line of action
	act in a common dimension
	pass through a common point
	act in a common plane

Solution

Collinear forces act along the same line of action, concurrent forces pass through a common point and coplanar forces act in a common plane.

Coplanar forces:

62% Answer Correctly

	act along the same line of action
	pass through a common point
	act in a common plane
	have opposite dimensions

Solution

Collinear forces act along the same line of action, concurrent forces pass through a common point and coplanar forces act in a common plane.

An object's resistance to changes in direction is known as:

82% Answer Correctly

	kinetic energy
	mass
	inertia
	weight

Solution

The more mass a substance has the more force is required to move it or to change its direction. This resistance to changes in direction is known as inertia.

4 If the force applied at the blue arrow over 7 ft. moves the green box 0.78 ft., what is the mechanical advantage of this lever?

56% Answer Correctly

	13.5
	14
	9.9
	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 = \( \frac{7 ft.}{0.78 ft.} \) = 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.

5 If you have a gear train with two gears, the first with 20 teeth and the second with 12 teeth, how many revolutions does the second gear make for each revolution of the first gear?

78% Answer Correctly

	1.7
	1.8
	0.8
	3.2

Solution

The gear ratio (V_r) of a gear train is the product of the gear ratios between the pairs of meshed gears. Let N represent the number of teeth for each gear:

V_r = \( \frac{N_1}{N_2} \) \( \frac{N_2}{N_3} \) \( \frac{N_3}{N_4} \) ... \( \frac{N_n}{N_{n+1}} \)

In this problem, we have only two gears so the equation becomes:

V_r = \( \frac{N_1}{N_2} \) = \( \frac{20}{12} \) = 1.7