ASVAB Mechanical Comprehension Practice Test 814086 Results

	Your Results	Global Average
Questions	5	5
Correct	0	2.65
Score	0%	53%

Review

1 If you have a gear train with three gears, the first with 26 teeth, the second with 10 teeth, and the third with 8 teeth, what is its mechanical advantage?

50% Answer Correctly

	-3.8
	3.3
	2.9
	4.9

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 = \( \frac{N_1}{N_2} \) \( \frac{N_2}{N_3} \) = \( \frac{26}{10} \) \( \frac{10}{8} \) = \( \frac{26}{8} \) = 3.3

2 A 370 lb. barrel is rolled up a 18 ft. ramp to a platform that's 2 ft. tall. What effort is required to move the barrel?

53% Answer Correctly

	123.3 lbs.
	61.7 lbs.
	20.6 lbs.
	41.1 lbs.

Solution

This problem describes an inclined plane and, for an inclined plane, the effort force multiplied by the effort distance equals the resistance force multipied by the resistance distance:

F_ed_e = F_rd_r

Plugging in the variables from this problem yields:

F_e x 18 ft. = 370 lbs. x 2 ft.
F_e = \( \frac{740 ft⋅lb}{18 ft.} \) = 41.1 lbs.

3 If the radius of the axle is 3 and the radius of the wheel is 6, what is the mechanical advantage of this wheel and axle configuration?

41% Answer Correctly

	3
	2.0
	6
	0.5

Solution

The mechanical advantage of a wheel and axle is the input radius divided by the output radius:

MA = \( \frac{r_i}{r_o} \)

In this case, the input radius (where the effort force is being applied) is 3 and the output radius (where the resistance is being applied) is 6 for a mechanical advantage of \( \frac{3}{6} \) = 0.5

4 The radius of the axle is 7, the radius of the wheel is 10, and the blue box weighs 50 lbs. What is the effort force necessary to balance the load?

53% Answer Correctly

	14.3 lbs.
	34.97 lbs.
	17 lbs.
	70 lbs.

Solution

The mechanical advantage of a wheel and axle is the input radius divided by the output radius:

MA = \( \frac{r_i}{r_o} \)

In this case, the input radius (where the effort force is being applied) is 10 and the output radius (where the resistance is being applied) is 7 for a mechanical advantage of \( \frac{10}{7} \) = 1.43

MA = \( \frac{load}{effort} \) so effort = \( \frac{load}{MA} \) = \( \frac{50 lbs.}{1.43} \) = 34.97 lbs.

A a seesaw / teeter-totter is an example of which of the following?

69% Answer Correctly

	third-class lever
	first-class lever
	second-class lever
	inclined plane

Solution

A first-class lever is used to increase force or distance while changing the direction of the force. The lever pivots on a fulcrum and, when a force is applied to the lever at one side of the fulcrum, the other end moves in the opposite direction. The position of the fulcrum also defines the mechanical advantage of the lever. If the fulcrum is closer to the force being applied, the load can be moved a greater distance at the expense of requiring a greater input force. If the fulcrum is closer to the load, less force is required but the force must be applied over a longer distance. An example of a first-class lever is a seesaw / teeter-totter.