ASVAB Mechanical Comprehension Practice Test 739467 Results

	Your Results	Global Average
Questions	5	5
Correct	0	3.40
Score	0%	68%

Review

1 20 lbs. of effort is used by a machine to lift a 100 lbs. box. What is the mechanical advantage of the machine?

84% Answer Correctly

	5
	10
	7
	6.5

Solution

Mechanical advantage is resistance force divided by effort force:

MA = \( \frac{F_r}{F_e} \) = \( \frac{100 lbs.}{20 lbs.} \) = 5

Specific gravity is a comparison of the density of an object with the density of:

57% Answer Correctly

	water
	air
	oil
	carbon

Solution

Specific gravity is the ratio of the density of equal volumes of a substance and water and is measured by a hyrdometer.

3 If you have a gear train with two gears, the first with 32 teeth and the second with 4 teeth, how many revolutions does the second gear make for each revolution of the first gear?

77% Answer Correctly

	16
	9.5
	8
	11

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 = \( \frac{N_1}{N_2} \) = \( \frac{32}{4} \) = 8

4 If 25 lbs. of force is applied 6 ft. from the fulcrum at the blue arrow and the green box is 3 ft. from the fulcrum, how much would the green box have to weigh to balance the lever?

62% Answer Correctly

	200 lbs.
	50 lbs.
	100 lbs.
	0 lbs.

Solution

To balance this lever the torques at the green box and the blue arrow 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 green box and b the blue arrow, R is resistance (weight/force) and d is the distance from the fulcrum.

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

R_a = \( \frac{R_bd_b}{d_a} \) = \( \frac{25 lbs. \times 6 ft.}{3 ft.} \) = \( \frac{150 ft⋅lb}{3 ft.} \) = 50 lbs.

Power is the rate at which:

62% Answer Correctly

	potential energy is converted into kinetic energy
	input force is transferred to output force
	friction is overcome
	work is done

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.