ASVAB Mechanical Comprehension Practice Test 930710 Results

Your Results Global Average
Questions 5 5
Correct 0 3.24
Score 0% 65%

Review

1 The green box weighs 15 lbs. and a 5 lbs. weight is placed 5 ft. from the fulcrum at the blue arrow. How far from the fulcrum would the green box need to be placed to balance the lever?
57% Answer Correctly
75 ft.
1.67 ft.
0.42 ft.
3.33 ft.
Solution

To balance this lever the torques on each side of the fulcrum must be equal. Torque is weight x distance from the fulcrum so the equation for equilibrium is:

Rada = Rbdb

where a represents the left side of the fulcrum and b the right, R is resistance (weight) and d is the distance from the fulcrum.

Solving for da, our missing value, and plugging in our variables yields:

da = \( \frac{R_bd_b}{R_a} \) = \( \frac{5 lbs. \times 5 ft.}{15 lbs.} \) = \( \frac{25 ft⋅lb}{15 lbs.} \) = 1.67 ft.

2

A fixed pulley has a mechanical advantage of:

68% Answer Correctly

-1

2

1

0
Solution

A fixed pulley is used to change the direction of a force and does not multiply the force applied. As such, it has a mechanical advantage of one. The benefit of a fixed pulley is that it can allow the force to be applied at a more convenient angle, for example, pulling downward or horizontally to lift an object instead of upward.

3

The mass of an object correlates to the size of the object but ultimately depends on:

66% Answer Correctly

the object's weight

gravity

the object's density

the object's potential energy
Solution

Mass is a measure of the amount of matter in an object.  In general, larger objects have larger mass than smaller objects but mass ultimately depends on how compact (dense) a substance is.

4 What's the mechanical advantage of a wedge that's 5 inches wide and 45 inches long?
83% Answer Correctly
27
13.5
12
9
Solution

The mechanical advantage (MA) of a wedge is its length divided by its thickness:

MA = \( \frac{l}{t} \) = \( \frac{45 in.}{5 in.} \) = 9

5 If you have a gear train with three gears, the first with 26 teeth, the second with 12 teeth, and the third with 2 teeth, what is its mechanical advantage?
51% Answer Correctly
19.5
13
6.5
14.5
Solution

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

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

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

Vr = \( \frac{N_1}{N_2} \) \( \frac{N_2}{N_3} \) = \( \frac{26}{12} \) \( \frac{12}{2} \) = \( \frac{26}{2} \) = 13