ASVAB Mechanical Comprehension Practice Test 504164 Results

Your Results Global Average
Questions 5 5
Correct 0 3.16
Score 0% 63%

Review

1 A = 9 ft., the green box weighs 20 lbs., and the blue box weighs 30 lbs. What does distance B need to be for this lever to balance?
65% Answer Correctly
1.5 ft.
6 ft.
0 ft.
24 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:

20 lbs. x 9 ft. = 30 lbs. x dB

dB = \( \frac{20 \times 9 ft⋅lb}{30 lbs.} \) = \( \frac{180 ft⋅lb}{30 lbs.} \) = 6 ft.

2

Which of the following is not a modulus of elasticity?

47% Answer Correctly

stress modulus

shear modulus

stretch modulus

bulk modulus
Solution

The modulus of elasticity measures how much a material or structure will deflect under stress. Stretch modulus is longitudinal stretch (like stretching raw bread dough), shear modulus is longitudinal deflection (like the horizontal displacement of a stack of magzines when a heavy object is placed upon them), and bulk modulus is compression of volume (like the compression of a loaf of bread under a heavy can at the bottom of a grocery bag).

3 What is the efficiency of a machine has work input of 250 ft⋅lb and work output of 225 ft⋅lb?
67% Answer Correctly
10%
22%
180%
90%
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:
\( Efficiency = \frac{Work_{out}}{Work_{in}} \times 100 \) \( = \frac{225 ft⋅lb}{250 ft⋅lb} \times 100 \) \( = 90% \) %
4 If you have a gear train with two gears, the first with 24 teeth and the second with 16 teeth, how many revolutions does the second gear make for each revolution of the first gear?
77% Answer Correctly
0.5
1.5
2.3
3.5
Solution

The gear ratio (Vr) of a gear train is the product of the gear ratios between the pairs of meshed gears. Let N represent the number of teeth for each gear:

Vr = \( \frac{N_1}{N_2} \) \( \frac{N_2}{N_3} \) \( \frac{N_3}{N_4} \) ... \( \frac{N_n}{N_{n+1}} \)

In this problem, we have only two gears so the equation becomes:

Vr = \( \frac{N_1}{N_2} \) = \( \frac{24}{16} \) = 1.5

5

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, decrease

decrease, increase

increase, increase

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.