ASVAB Mechanical Comprehension Practice Test 408931 Results

	Your Results	Global Average
Questions	5	5
Correct	0	3.00
Score	0%	60%

Review

1 If the handles of a wheelbarrow are 1.0 ft. from the wheel axle and the load is concentrated at a point 1.5 ft. from the axle, how many pounds of load will a 190 lbs. force lift?

47% Answer Correctly

	190
	126.7
	24
	-30

Solution

This problem describes a second-class lever and, for a second class lever, the effort force multiplied by the effort distance equals the resistance force multipied by the resistance distance: F_ed_e = F_rd_r. In this problem we're looking for resistance force:
\( F_r = \frac{F_e d_e}{d_r} \)
\( F_r = \frac{190 \times 1.0}{1.5} \)
\( F_r = \frac{190.0}{1.5} \)
\( F_r = 126.7 \)

Which of these is the formula for kinetic energy?

68% Answer Correctly

	\(KE = {m \over v^2 }\)
	\(KE = {1 \over 2}mv^2\)
	\(KE = mgh\)
	\(KE = {1 \over 2}mh^2\)

Solution

Kinetic energy is the energy of movement and is a function of the mass of an object and its speed: \(KE = {1 \over 2}mv^2\) where m is mass in kilograms, v is speed in meters per second, and KE is in joules. The most impactful quantity to kinetic energy is velocity as an increase in mass increases KE linearly while an increase in speed increases KE exponentially.

3 If you have a gear train with two gears, the first with 40 teeth and the second with 16 teeth, how many revolutions does the second gear make for each revolution of the first gear?

77% Answer Correctly

	2.3
	0.8
	1.3
	2.5

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 = \( \frac{N_1}{N_2} \) = \( \frac{40}{16} \) = 2.5

4 If you have a gear train with three gears, the first with 24 teeth, the second with 16 teeth, and the third with 6 teeth, what is its mechanical advantage?

50% Answer Correctly

	2
	6
	4
	4.4

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 = \( \frac{N_1}{N_2} \) \( \frac{N_2}{N_3} \) = \( \frac{24}{16} \) \( \frac{16}{6} \) = \( \frac{24}{6} \) = 4

A shovel is an example of which class of lever?

56% Answer Correctly

	third
	second
	a shovel is not a lever
	first

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.