ASVAB Mechanical Comprehension Practice Test 517079 Results

Your Results Global Average
Questions 5 5
Correct 0 2.88
Score 0% 58%

Review

1 If A = 4 ft. and the green box weighs 5 lbs. what is the torque acting on the A side of this lever?
74% Answer Correctly
5 ft⋅lb
80 ft⋅lb
20 ft⋅lb
60 ft⋅lb
Solution
For a lever, torque is weight x distance from the fulcrum which, in this case, is: 5 ft. x 4 lbs. = 20 ft⋅lb
2 If the radius of the axle is 3 and the radius of the wheel is 6, what is the mechanical advantage of this wheel and axle configuration?
41% Answer Correctly
0.5
6
-3
2.0
Solution

The mechanical advantage of a wheel and axle is the input radius divided by the output radius:

MA = \( \frac{r_i}{r_o} \)

In this case, the input radius (where the effort force is being applied) is 3 and the output radius (where the resistance is being applied) is 6 for a mechanical advantage of \( \frac{3}{6} \) = 0.5

3

Gear ratio indicates which of the following about two connected gears?

59% Answer Correctly

work done

power conversion

mechanical advantage

efficiency
Solution

The mechanical advantage (amount of change in speed or torque) of connected gears is proportional to the number of teeth each gear has. Called gear ratio, it's the ratio of the number of teeth on the larger gear to the number of teeth on the smaller gear.  For example, a gear with 12 teeth connected to a gear with 9 teeth would have a gear ratio of 4:3.

4 What is the efficiency of a machine has work input of 80 ft⋅lb and work output of 48 ft⋅lb?
67% Answer Correctly
60%
0%
120%
40%
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:
\( Efficiency = \frac{Work_{out}}{Work_{in}} \times 100 \) \( = \frac{48 ft⋅lb}{80 ft⋅lb} \times 100 \) \( = 60% \) %
5 If A = 10 ft., B = 1 ft., C = 9 ft., the green box weighs 45 lbs. and the blue box weighs 50 lbs., what does the orange box have to weigh for this lever to balance?
44% Answer Correctly
22.22 lbs.
450 lbs.
44.44 lbs.
45 lbs.
Solution
In order for this lever to balance, the torque acting on each side of the fulrum must be equal. So, the torque produced by A must equal the torque produced by B and C. Torque is weight x distance from the fulcrum which means that the following must be true for the lever to balance:

fAdA = fBdB + fCdC

For this problem, this equation becomes:

45 lbs. x 10 ft. = 50 lbs. x 1 ft. + fC x 9 ft.

450 ft. lbs. = 50 ft. lbs. + fC x 9 ft.

fC = \( \frac{450 ft. lbs. - 50 ft. lbs.}{9 ft.} \) = \( \frac{400 ft. lbs.}{9 ft.} \) = 44.44 lbs.