ASVAB Mechanical Comprehension Practice Test 38800 Results

Your Results Global Average
Questions 5 5
Correct 0 2.83
Score 0% 57%

Review

1 If the green box weighs 15 lbs. and is 6 ft. from the fulcrum, how much force would need to be applied at the blue arrow to balance the lever if the arrow's distance from the fulcrum is 9 ft.?
62% Answer Correctly
40 lbs.
1 lbs.
0 lbs.
10 lbs.
Solution

To balance this lever the torques at the green box and the blue arrow must be equal. Torque is weight x distance from the fulcrum so the equation for equilibrium is:

Rada = Rbdb

where a represents the green box and b the blue arrow, R is resistance (weight/force) and d is the distance from the fulcrum.

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

Rb = \( \frac{R_ad_a}{d_b} \) = \( \frac{15 lbs. \times 6 ft.}{9 ft.} \) = \( \frac{90 ft⋅lb}{9 ft.} \) = 10 lbs.

2 If you have a gear train with two gears, the first with 36 teeth and the second with 4 teeth, how many revolutions does the second gear make for each revolution of the first gear?
77% Answer Correctly
3
27
9
8
Solution

The gear ratio (Vr) 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:

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 only two gears so the equation becomes:

Vr = \( \frac{N_1}{N_2} \) = \( \frac{36}{4} \) = 9

3

Depending on where you apply effort and resistance, the wheel and axle can multiply:

45% Answer Correctly

speed or power

force or speed

power or distance

force or distance
Solution

If you apply the resistance to the axle and the effort to the wheel, the wheel and axle will multiply force and if you apply the resistance to the wheel and the effort to the axle, it will multiply speed.

4 If you have a gear train with three gears, the first with 30 teeth, the second with 12 teeth, and the third with 4 teeth, what is its mechanical advantage?
51% Answer Correctly
7.5
15
6.8
4.5
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 = \( \frac{N_1}{N_2} \) \( \frac{N_2}{N_3} \) = \( \frac{30}{12} \) \( \frac{12}{4} \) = \( \frac{30}{4} \) = 7.5

5 If the handles of a wheelbarrow are 1.0 ft. from the wheel axle and the load is concentrated at a point 0.5 ft. from the axle, how many pounds of load will a 200 lbs. force lift?
47% Answer Correctly
70.9
-99
400
100
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: Fede = Frdr. In this problem we're looking for resistance force:
\( F_r = \frac{F_e d_e}{d_r} \)
\( F_r = \frac{200 \times 1.0}{0.5} \)
\( F_r = \frac{200.0}{0.5} \)
\( F_r = 400 \)