ASVAB Mechanical Comprehension Practice Test 156751 Results

	Your Results	Global Average
Questions	5	5
Correct	0	3.55
Score	0%	71%

Review

1 If you have a gear train with two gears, the first with 40 teeth and the second with 8 teeth, how many revolutions does the second gear make for each revolution of the first gear?

78% Answer Correctly

	5
	1.7
	12
	-1

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 = \( \frac{N_1}{N_2} \) = \( \frac{40}{8} \) = 5

2 If the green arrow in this diagram represents 390 ft⋅lb of work, how far will the box move if it weighs 130 pounds?

73% Answer Correctly

	3 ft.
	32 ft.
	1 ft.
	43 ft.

Solution

The Law of Work states that the work put into a machine is equal to the work received from the machine under ideal conditions. In equation form, that's:

W_in = W_out
F_effort x d_effort = F_resistance x d_resistance

In this problem, the effort work is 390 ft⋅lb and the resistance force is 130 lbs. and we need to calculate the resistance distance:

W_in = F_resistance x d_resistance
390 ft⋅lb = 130 lbs. x d_resistance
d_resistance = \( \frac{390ft⋅lb}{130 lbs.} \) = 3 ft.

3 How much resistance could a 60 lb. effort force lift using a block and tackle pulley that has 8 ropes supporting the resistance?

82% Answer Correctly

	480 lbs.
	432 lbs.
	474 lbs.
	528 lbs.

Solution

The mechanical advantage (MA) of a block and tackle pulley is equal to the number of times the effort force changes direction. An easy way to count how many times the effort force changes direction is to count the number of ropes that support the resistance which, in this problem, is 8. With a MA of 8, a 60 lbs. effort force could lift 60 lbs. x 8 = 480 lbs. resistance.

Potential energy is energy that has the potential to be converted into what?

81% Answer Correctly

	power
	heat
	work
	kinetic energy

Solution

Potential energy is the energy of an object by virtue of its position relative to other objects. It is energy that has the potential to be converted into kinetic energy.

5 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

	6
	3
	0.5
	-3

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