ASVAB Mechanical Comprehension Practice Test 556266 Results

Your Results Global Average
Questions 5 5
Correct 0 3.09
Score 0% 62%

Review

1 What is the efficiency of a machine has work input of 140 ft⋅lb and work output of 119 ft⋅lb?
67% Answer Correctly
85%
15%
1%
340%
Solution
Due to friction, a machine will never be able to utilize 100% of its work input. A certain percentage of that input will be lost in overcoming friction within the machine. Effeciency is a measure of how much of a machine's work input can be turned into useful work output and is calculated by dividing work output by work input and multiplying the result by 100:
\( Efficiency = \frac{Work_{out}}{Work_{in}} \times 100 \) \( = \frac{119 ft⋅lb}{140 ft⋅lb} \times 100 \) \( = 85% \) %
2 If the green box weighs 60 lbs. and is 3 ft. from the fulcrum, how far from the fulcrum would a 60 lbs. weight need to be placed to balance the lever?
61% Answer Correctly
12 ft.
20 ft.
0.75 ft.
3 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 db, our missing value, and plugging in our variables yields:

db = \( \frac{R_ad_a}{R_b} \) = \( \frac{60 lbs. \times 3 ft.}{60 lbs.} \) = \( \frac{180 ft⋅lb}{60 lbs.} \) = 3 ft.

3

Two or more pulleys used together are called:

71% Answer Correctly

wheel and axle

gears

third-class lever

block and tackle
Solution

Two or more pulleys used together constitute a block and tackle which, unlike a fixed pulley, does impart mechanical advantage as a function of the number of pulleys that make up the arrangement.  So, for example, a block and tackle with three pulleys would have a mechanical advantage of three.

4 If the handles of a wheelbarrow are 1.0 ft. from the wheel axle, how many pounds of force must you exert to lift the handles if it's carrying a 230 lbs. load concentrated at a point 0.5 ft. from the axle?
52% Answer Correctly
115
0
70
184.4
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 effort force:
\( F_e = \frac{F_r d_r}{d_e} \)
\( F_e = \frac{230 \times 0.5}{1.0} \)
\( F_e = \frac{115.0}{1.0} \)
\( F_e = 115 \)
5

Which of the following is the formula for hydraulic pressure?

58% Answer Correctly

P = F/A2

P = FA2

P = F/A

P = FA
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).