ASVAB Mechanical Comprehension Practice Test 133713 Results

	Your Results	Global Average
Questions	5	5
Correct	0	2.74
Score	0%	55%

Review

Gear ratio indicates which of the following about two connected gears?

59% Answer Correctly

	mechanical advantage
	work done
	power conversion
	efficiency

Solution

The mechanical advantage (amount of change in speed or torque) of connected gears is proportional to the number of teeth each gear has. Called gear ratio, it's the ratio of the number of teeth on the larger gear to the number of teeth on the smaller gear. For example, a gear with 12 teeth connected to a gear with 9 teeth would have a gear ratio of 4:3.

2 If A = 8 ft., B = 3 ft., C = 4 ft., the green box weighs 50 lbs. and the blue box weighs 60 lbs., what does the orange box have to weigh for this lever to balance?

44% Answer Correctly

	27.5 lbs.
	55 lbs.
	13.75 lbs.
	110 lbs.

Solution

In order for this lever to balance, the torque acting on each side of the fulrum must be equal. So, the torque produced by A must equal the torque produced by B and C. Torque is weight x distance from the fulcrum which means that the following must be true for the lever to balance:

f_Ad_A = f_Bd_B + f_Cd_C

For this problem, this equation becomes:

50 lbs. x 8 ft. = 60 lbs. x 3 ft. + f_C x 4 ft.

400 ft. lbs. = 180 ft. lbs. + f_C x 4 ft.

f_C = \( \frac{400 ft. lbs. - 180 ft. lbs.}{4 ft.} \) = \( \frac{220 ft. lbs.}{4 ft.} \) = 55 lbs.

3 If a 40 lbs. weight is placed 9 ft. from the fulcrum at the blue arrow and the green box is 8 ft. from the fulcrum, how much would the green box have to weigh to balance the lever?

61% Answer Correctly

	0 lbs.
	4 lbs.
	45 lbs.
	180 lbs.

Solution

To balance this lever the torques on each side of the fulcrum 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 left side of the fulcrum and b the right, R is resistance (weight) and d is the distance from the fulcrum.

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

R_a = \( \frac{R_bd_b}{d_a} \) = \( \frac{40 lbs. \times 9 ft.}{8 ft.} \) = \( \frac{360 ft⋅lb}{8 ft.} \) = 45 lbs.

Which of these will have the most impact on the kinetic energy of an object?

54% Answer Correctly

	its speed
	its weight
	its direction
	its mass

Solution

Kinetic energy is the energy of movement and is a function of the mass of an object and its speed: \(KE = {1 \over 2}mv^2\) where m is mass in kilograms, v is speed in meters per second, and KE is in joules. The most impactful quantity to kinetic energy is velocity as an increase in mass increases KE linearly while an increase in speed increases KE exponentially.

The principle of moments defines equilibrium in terms of:

54% Answer Correctly

	power
	speed
	torque
	energy

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.