ASVAB Mechanical Comprehension Practice Test 595105 Results

	Your Results	Global Average
Questions	5	5
Correct	0	2.86
Score	0%	57%

Review

The force required to initally get an object moving is __________ the force required to keep it moving.

76% Answer Correctly

	the same as
	lower than
	higher than
	opposite

Solution

For any given surface, the coefficient of static friction is higher than the coefficient of kinetic friction. More force is required to initally get an object moving than is required to keep it moving. Additionally, static friction only arises in response to an attempt to move an object (overcome the normal force between it and the surface).

2 If the radius of the axle is 7 and the radius of the wheel is 10, what is the mechanical advantage of this wheel and axle configuration?

36% Answer Correctly

	1
	1
	7
	-3

Solution

The mechanical advantage of a wheel and axle lies in the difference in radius between the inner (axle) wheel and the outer wheel. But, this mechanical advantage is only realized when the input effort and load are applied to different wheels. Applying both input effort and load to the same wheel results in a mechanical advantage of 1.

Boyle's law defines the relationship between pressure and volume as:

57% Answer Correctly

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

Solution

Boyle's law states that "for a fixed amount of an ideal gas kept at a fixed temperature, pressure and volume are inversely proportional". Expressed as a formula, that's \(\frac{P_1}{P_2} = \frac{V_2}{V_1}\)

4 If the green box is 2 ft. from the fulcrum and a certain force applied 6 ft. from the fulcrum at the blue arrow balances the lever, what is the mechanical advantage?

61% Answer Correctly

	3
	5
	1.5
	2.7

Solution

Because this lever is in equilibrium, we know that the effort force at the blue arrow is equal to the resistance weight of the green box. For a lever that's in equilibrium, one method of calculating mechanical advantage (MA) is to divide the length of the effort arm (E_a) by the length of the resistance arm (R_a):

MA = \( \frac{E_a}{R_a} \) = \( \frac{6 ft.}{2 ft.} \) = 3

When a lever is in equilibrium, the torque from the effort and the resistance are equal. The equation for equilibrium is R_ad_a = R_bd_b where a and b are the two points at which effort/resistance is being applied to the lever.

In this problem, R_a and R_b are such that the lever is in equilibrium meaning that some multiple of the weight of the green box is being applied at the blue arrow. For a lever, this multiple is a function of the ratio of the distances of the box and the arrow from the fulcrum. That's why, for a lever in equilibrium, only the distances from the fulcrum are necessary to calculate mechanical advantage.

If the lever were not in equilibrium, you would first have to calculate the forces and distances necessary to put it in equilibrium and then divide E_a by R_a to get the mechanical advantage.

5 A mass of air has a pressure of 15.0 psi and a volume of 75 ft.³. If the air is compressed to a new volume of 50 ft.³, what is the new pressure?

56% Answer Correctly

	7.5 psi
	24.8 psi
	22.5 psi
	25.5 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 = 50 ft.³, V₁ = 75 ft.³ and P₁ = 15.0 psi. Solving for P₂:

P₂ = \( \frac{P_1}{\frac{V_2}{V_1}} \) = \( \frac{15.0 psi}{\frac{50 ft.^3}{75 ft.^3}} \) = 22.5 psi