ASVAB Mechanical Comprehension Practice Test 396086 Results

Your Results Global Average
Questions 5 5
Correct 0 2.81
Score 0% 56%

Review

1 If the handles of a wheelbarrow are 0.5 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 240 lbs. force lift?
47% Answer Correctly
720
80
360
120
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:
\( F_r = \frac{F_e d_e}{d_r} \)
\( F_r = \frac{240 \times 0.5}{1.5} \)
\( F_r = \frac{120.0}{1.5} \)
\( F_r = 80 \)
2 If you have a gear train with three gears, the first with 30 teeth, the second with 12 teeth, and the third with 6 teeth, what is its mechanical advantage?
50% Answer Correctly
5.5
7
5
8
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 = \( \frac{N_1}{N_2} \) \( \frac{N_2}{N_3} \) = \( \frac{30}{12} \) \( \frac{12}{6} \) = \( \frac{30}{6} \) = 5

3

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.

4 What is the power output of a 7 hp engine that's 35% efficient?
40% Answer Correctly
1347.5 \( \frac{ft⋅lb}{s} \)
245 \( \frac{ft⋅lb}{s} \)
2695 \( \frac{ft⋅lb}{s} \)
5 \( \frac{ft⋅lb}{s} \)
Solution
\( Efficiency = \frac{Power_{out}}{Power_{in}} \times 100 \)
Solving for power out: \( P_{o} = \frac{E \times P_{i}}{100} \)
Knowing that 1 hp = 550 \( \frac{ft⋅lb}{s} \), Pi becomes 7 hp x 550 \( \frac{ft⋅lb}{s} \) = 3850 \( \frac{ft⋅lb}{s} \)
\( P_{o} = \frac{E \times P_{i}}{100} = \frac{35 \times 3850 \frac{ft⋅lb}{s}}{100} \) \( = \frac{134750 \frac{ft⋅lb}{s}}{100} \) = 1347.5 \( \frac{ft⋅lb}{s} \)
5

Hydraulics is the transmission of force through the use of which of the following?

73% Answer Correctly

air pressure

gear systems

torque

liquids
Solution

Hydraulics is the transmission of force through the use of liquids. Liquids are especially suited for transferring force in complex machines because they compress very little and can occupy very small spaces. Hydraulic pressure is calculated by dividing force by the area over which it is applied: P = F/A where F is force in pounds, A is area in square inches, and the resulting pressure is in pounds per square inch (psi).