ASVAB Mechanical Comprehension Practice Test 39863 Results

	Your Results	Global Average
Questions	5	5
Correct	0	2.59
Score	0%	52%

Review

1 If the handles of a wheelbarrow are 2.5 ft. from the wheel axle and the load is concentrated at a point 1.0 ft. from the axle, how many pounds of load will a 230 lbs. force lift?

47% Answer Correctly

	210.6
	-87
	575
	-23.4

Solution

This problem describes a second-class lever and, for a second class lever, the effort force multiplied by the effort distance equals the resistance force multipied by the resistance distance: F_ed_e = F_rd_r. In this problem we're looking for resistance force:
\( F_r = \frac{F_e d_e}{d_r} \)
\( F_r = \frac{230 \times 2.5}{1.0} \)
\( F_r = \frac{575.0}{1.0} \)
\( F_r = 575 \)

A watt is the unit for which of the following?

71% Answer Correctly

	power
	work
	energy
	mechanical advantage

Solution

Power is the rate at which work is done, P = w/t, or work per unit time. The watt (W) is the unit for power and is equal to 1 joule (or newton-meter) per second. Horsepower (hp) is another familiar unit of power used primarily for rating internal combustion engines. 1 hp equals 746 watts.

The mechanical advantage of a third class lever is always:

37% Answer Correctly

	equal to one
	not equal to one
	less than one
	greater than one

Solution

A third class lever is designed to multiply distance and speed at the expense of effort force. Because the effort force is greater than the resistance, the mechanical advantage of a third class lever is always less than one.

An example of a third class lever is a broom. The fulcrum is at your hand on the end of the broom, the effort force is your other hand in the middle, and the resistance is at the bottom bristles. The effort force of your hand in the middle multiplies the distance and speed of the bristles at the bottom but at the expense of producing a brushing force that's less than the force you're applying with your hand.

4 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?

57% Answer Correctly

	11.3 psi
	22.5 psi
	28.5 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

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

	3
	6
	2.0
	0.5

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