ASVAB Mechanical Comprehension Practice Test 183202 Results

	Your Results	Global Average
Questions	5	5
Correct	0	2.66
Score	0%	53%

Review

The mechanical advantage of a third class lever is always:

37% Answer Correctly

	greater than one
	equal to one
	less than one
	not equal to one

Solution

A third class lever is designed to multiply distance and speed at the expense of effort force. Because the effort force is greater than the resistance, the mechanical advantage of a third class lever is always less than one.

An example of a third class lever is a broom. The fulcrum is at your hand on the end of the broom, the effort force is your other hand in the middle, and the resistance is at the bottom bristles. The effort force of your hand in the middle multiplies the distance and speed of the bristles at the bottom but at the expense of producing a brushing force that's less than the force you're applying with your hand.

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

50% Answer Correctly

	wheel and axle
	first-class lever
	inclined plane
	block and tackle

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.

3 If you have a gear train with three gears, the first with 30 teeth, the second with 16 teeth, and the third with 6 teeth, what is its mechanical advantage?

51% Answer Correctly

	6.5
	5
	5.5
	1.7

Solution

The mechanical advantage of a gear train is its gear ratio. The gear ratio (V_r) 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 three gears so the equation becomes:

V_r = \( \frac{N_1}{N_2} \) \( \frac{N_2}{N_3} \) = \( \frac{30}{16} \) \( \frac{16}{6} \) = \( \frac{30}{6} \) = 5

The force exerted on an object due to gravity is called:

70% Answer Correctly

	density
	potential energy
	weight
	mass

Solution

Mass is an intrinsic property of matter and does not vary. Weight is the force exerted on the mass of an object due to gravity and a specific case of Newton's Second Law of Motion. Replace force with weight and acceleration with acceleration due to gravity on Earth (g) and the result is the formula for weight: W = mg or, substituting for g, weight equals mass multiplied by 9.8 m/s².

5 How much work can a 2 hp engine do in 7 seconds?

52% Answer Correctly

	4 ft⋅lb
	3 ft⋅lb
	0 ft⋅lb
	7700 ft⋅lb

Solution

Horsepower (hp) is a common measure of power output for complex machines. By definition, a 1 hp machine does 550 ft⋅lb of work in 1 second: 1 hp = 550 ft⋅lb/s. Substituting the variables for this problem gives us:
\( W = 2 hp \times 550 \frac{ft⋅lb}{s} \times 7s = 7700 ft⋅lb \)