ASVAB Mechanical Comprehension Practice Test 39932 Results

	Your Results	Global Average
Questions	5	5
Correct	0	3.08
Score	0%	62%

Review

1 How much work can a 7 hp engine do in 6 seconds?

52% Answer Correctly

	28 ft⋅lb
	14 ft⋅lb
	23100 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:
\( W = 7 hp \times 550 \frac{ft⋅lb}{s} \times 6s = 23100 ft⋅lb \)

Which of the following will increase the mechanical advantage of this inclined plane?

59% Answer Correctly

	lengthen the ramp
	increase the force acting at the blue arrow
	shorten the ramp
	lower the force acting at the blue arrow

Solution

The mechanical advantage (MA) of an inclined plane is the effort distance divided by the resistance distance. In order to increase mechanical advantage, this ratio must increase which means making the effort distance longer and this can be accomplished by lengthening the length of the ramp.

3 If a 50 lbs. weight is placed 1 ft. from the fulcrum at the blue arrow and the green box is 8 ft. from the fulcrum, how much would the green box have to weigh to balance the lever?

61% Answer Correctly

	6.25 lbs.
	12.5 lbs.
	0 lbs.
	1.56 lbs.

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:

R_ad_a = R_bd_b

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 R_a, our missing value, and plugging in our variables yields:

R_a = \( \frac{R_bd_b}{d_a} \) = \( \frac{50 lbs. \times 1 ft.}{8 ft.} \) = \( \frac{50 ft⋅lb}{8 ft.} \) = 6.25 lbs.

4 If you have a gear train with two gears, the first with 36 teeth and the second with 12 teeth, how many revolutions does the second gear make for each revolution of the first gear?

77% Answer Correctly

	1.5
	9
	3.3
	3

Solution

The gear ratio (V_r) 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:

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

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

V_r = \( \frac{N_1}{N_2} \) = \( \frac{36}{12} \) = 3

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

59% Answer Correctly

	mechanical advantage
	efficiency
	work done
	power conversion

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.