ASVAB Mechanical Comprehension Practice Test 688391 Results

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

Review

1 A mass of air has a pressure of 9.0 psi and a volume of 45 ft.³. If the air is compressed to a new volume of 35 ft.³, what is the new pressure?

56% Answer Correctly

	3.9 psi
	11.6 psi
	12.7 psi
	6.6 psi

Solution

According to Boyle's Law, pressure and volume are inversely proportional:

\( \frac{P_1}{P_2} \) = \( \frac{V_2}{V_1} \)

In this problem, V₂ = 35 ft.³, V₁ = 45 ft.³ and P₁ = 9.0 psi. Solving for P₂:

P₂ = \( \frac{P_1}{\frac{V_2}{V_1}} \) = \( \frac{9.0 psi}{\frac{35 ft.^3}{45 ft.^3}} \) = 11.6 psi

2 How much resistance could a 30 lb. effort force lift using a block and tackle pulley that has 4 ropes supporting the resistance?

81% Answer Correctly

	125 lbs.
	108 lbs.
	120 lbs.
	40 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 4. With a MA of 4, a 30 lbs. effort force could lift 30 lbs. x 4 = 120 lbs. resistance.

When all forces acting on a system cancel each other out, this is called:

80% Answer Correctly

	rest
	stasis
	equilibrium
	potential energy

Solution

When a system is stable or balanced (equilibrium) all forces acting on the system cancel each other out. In the case of torque, equilibrium means that the sum of the anticlockwise moments about a center of rotation equal the sum of the clockwise moments.

A screw is most like which of the following other simple machines?

50% Answer Correctly

	inclined plane
	first-class lever
	block and tackle
	wheel and axle

Solution

A screw is an inclined plane wrapped in ridges (threads) around a cylinder. The distance between these ridges defines the pitch of the screw and this distance is how far the screw advances when it is turned once. The mechanical advantage of a screw is its circumference divided by the pitch.

The principle of moments defines equilibrium in terms of:

54% Answer Correctly

	energy
	power
	torque
	speed

Solution

According to the principle of moments, you can maintain equilibrium if the moments (forces) tending to clockwise rotation are equal to the moments tending to counterclockwise rotation. Another name for these moments of force is torque.