ASVAB Mechanical Comprehension Practice Test 821565 Results

Your Results Global Average
Questions 5 5
Correct 0 2.73
Score 0% 55%

Review

1

Which of the following is not a characteristic of a ceramic?

61% Answer Correctly

high melting point

low corrosive action

low density

chemically stable
Solution

Ceramics are mixtures of metallic and nonmetallic elements that withstand exteme thermal, chemical, and pressure environments. They have a high melting point, low corrosive action, and are chemically stable. Examples include rock, sand, clay, glass, brick, and porcelain.

2 The green box weighs 40 lbs. and a 15 lbs. weight is placed 1 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
0.75 ft.
1.5 ft.
0.38 ft.
40 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 = \( \frac{R_bd_b}{R_a} \) = \( \frac{15 lbs. \times 1 ft.}{40 lbs.} \) = \( \frac{15 ft⋅lb}{40 lbs.} \) = 0.38 ft.

3 What is the power output of a 4 hp engine that's 80% efficient?
40% Answer Correctly
5280 \( \frac{ft⋅lb}{s} \)
1760 \( \frac{ft⋅lb}{s} \)
586.7 \( \frac{ft⋅lb}{s} \)
7040 \( \frac{ft⋅lb}{s} \)
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 4 hp x 550 \( \frac{ft⋅lb}{s} \) = 2200 \( \frac{ft⋅lb}{s} \)
\( P_{o} = \frac{E \times P_{i}}{100} = \frac{80 \times 2200 \frac{ft⋅lb}{s}}{100} \) \( = \frac{176000 \frac{ft⋅lb}{s}}{100} \) = 1760 \( \frac{ft⋅lb}{s} \)
4

Two gears are connected and the smaller gear drives the larger gear. The speed of rotation will __________ and the torque will __________.

61% Answer Correctly

decrease, increase

increase, increase

decrease, decrease

increase, decrease
Solution

Connected gears of different numbers of teeth are used together to change the rotational speed and torque of the input force. If the smaller gear drives the larger gear, the speed of rotation will be reduced and the torque will increase. If the larger gear drives the smaller gear, the speed of rotation will increase and the torque will be reduced.

5 How much work can a 5 hp engine do in 6 seconds?
52% Answer Correctly
16500 ft⋅lb
1 ft⋅lb
20 ft⋅lb
0 ft⋅lb
Solution
Horsepower (hp) is a common measure of power output for complex machines. By definition, a 1 hp machine does 550 ft⋅lb of work in 1 second: 1 hp = 550 ft⋅lb/s. Substituting the variables for this problem gives us:
\( W = 5 hp \times 550 \frac{ft⋅lb}{s} \times 6s = 16500 ft⋅lb \)