ASVAB Mechanical Comprehension Practice Test 810816 Results

Your Results Global Average
Questions 5 5
Correct 0 3.29
Score 0% 66%

Review

1

When all forces acting on a system cancel each other out, this is called:

80% Answer Correctly

rest

stasis

equilibrium

potential energy
Solution

When a system is stable or balanced (equilibrium) all forces acting on the system cancel each other out. In the case of torque, equilibrium means that the sum of the anticlockwise moments about a center of rotation equal the sum of the clockwise moments.

2

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

73% Answer Correctly

torque

liquids

air pressure

gear systems
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).

3 The green box weighs 65 lbs. and a 40 lbs. weight is placed 9 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 ft.
5.54 ft.
7 ft.
1.38 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 = \( \frac{R_bd_b}{R_a} \) = \( \frac{40 lbs. \times 9 ft.}{65 lbs.} \) = \( \frac{360 ft⋅lb}{65 lbs.} \) = 5.54 ft.

4 A = 4 ft., the green box weighs 5 lbs., and the blue box weighs 30 lbs. What does distance B need to be for this lever to balance?
65% Answer Correctly
0.67 ft.
7 ft.
0.33 ft.
1 ft.
Solution
In order for this lever to balance, the torque acting on side A must equal the torque acting on side B. Torque is weight x distance from the fulcrum which means that the following must be true for the lever to balance:

fAdA = fBdB

For this problem, the equation becomes:

5 lbs. x 4 ft. = 30 lbs. x dB

dB = \( \frac{5 \times 4 ft⋅lb}{30 lbs.} \) = \( \frac{20 ft⋅lb}{30 lbs.} \) = 0.67 ft.

5 How much work can a 4 hp engine do in 4 seconds?
52% Answer Correctly
16 ft⋅lb
2 ft⋅lb
8800 ft⋅lb
1 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:
\( W = 4 hp \times 550 \frac{ft⋅lb}{s} \times 4s = 8800 ft⋅lb \)