ASVAB Mechanical Comprehension Practice Test 605742 Results

Your Results Global Average
Questions 5 5
Correct 0 3.22
Score 0% 64%

Review

1 What's the mechanical advantage of a wedge that's 5 inches wide and 35 inches long?
83% Answer Correctly
8.5
10
16
7
Solution

The mechanical advantage (MA) of a wedge is its length divided by its thickness:

MA = \( \frac{l}{t} \) = \( \frac{35 in.}{5 in.} \) = 7

2 What is the efficiency of a machine has work input of 160 ft⋅lb and work output of 96 ft⋅lb?
67% Answer Correctly
0%
30%
40%
60%
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:
\( Efficiency = \frac{Work_{out}}{Work_{in}} \times 100 \) \( = \frac{96 ft⋅lb}{160 ft⋅lb} \times 100 \) \( = 60% \) %
3 20 lbs. of effort is used by a machine to lift a 160 lbs. box. What is the mechanical advantage of the machine?
84% Answer Correctly
8
7.2
8.8
16
Solution

Mechanical advantage is resistance force divided by effort force:

MA = \( \frac{F_r}{F_e} \) = \( \frac{160 lbs.}{20 lbs.} \) = 8

4 If the radius of the axle is 7 and the radius of the wheel is 8, what is the mechanical advantage of this wheel and axle configuration?
36% Answer Correctly
-1
1
1
0
Solution

The mechanical advantage of a wheel and axle lies in the difference in radius between the inner (axle) wheel and the outer wheel. But, this mechanical advantage is only realized when the input effort and load are applied to different wheels. Applying both input effort and load to the same wheel results in a mechanical advantage of 1.

5 A 370 lb. barrel is rolled up a 13 ft. ramp to a platform that's 4 ft. tall. What effort is required to move the barrel?
53% Answer Correctly
227.7 lbs.
56.9 lbs.
122.8 lbs.
113.8 lbs.
Solution

This problem describes an inclined plane and, for an inclined plane, the effort force multiplied by the effort distance equals the resistance force multipied by the resistance distance:

Fede = Frdr

Plugging in the variables from this problem yields:

Fe x 13 ft. = 370 lbs. x 4 ft.
Fe = \( \frac{1480 ft⋅lb}{13 ft.} \) = 113.8 lbs.