ASVAB Mechanical Comprehension Practice Test 812687 Results

	Your Results	Global Average
Questions	5	5
Correct	0	2.73
Score	0%	55%

Review

Which of the following is the formula for gravitational potential energy?

61% Answer Correctly

	\(PE = { 1 \over 2} mg^2\)
	\(PE = mg^2h\)
	\(PE = mgh\)
	\(PE = { 1 \over 2} mv^2\)

Solution

Gravitational potential energy is energy by virtue of gravity. The higher an object is raised above a surface the greater the distance it must fall to reach that surface and the more velocity it will build as it falls. For gravitational potential energy, PE = mgh where m is mass (kilograms), h is height (meters), and g is acceleration due to gravity which is a constant (9.8 m/s²).

Which of the following is not a characteristic of a ceramic?

60% Answer Correctly

	low corrosive action
	low density
	high melting point
	chemically stable

Solution

Ceramics are mixtures of metallic and nonmetallic elements that withstand exteme thermal, chemical, and pressure environments. They have a high melting point, low corrosive action, and are chemically stable. Examples include rock, sand, clay, glass, brick, and porcelain.

Which of the following represents how much two materials resist sliding across each other?

53% Answer Correctly

	kinetic friction
	normal friction
	coefficient of friction
	static friction

Solution

Coefficient of friction (μ) represents how much two materials resist sliding across each other. Smooth surfaces like ice have low coefficients of friction while rough surfaces like concrete have high μ.

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

54% Answer Correctly

	its direction
	its mass
	its weight
	its speed

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.

5 If A = 8 ft., B = 2 ft., C = 7 ft., the green box weighs 45 lbs. and the blue box weighs 60 lbs., what does the orange box have to weigh for this lever to balance?

44% Answer Correctly

	90 lbs.
	34.29 lbs.
	102.86 lbs.
	68.57 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:

45 lbs. x 8 ft. = 60 lbs. x 2 ft. + f_C x 7 ft.

360 ft. lbs. = 120 ft. lbs. + f_C x 7 ft.

f_C = \( \frac{360 ft. lbs. - 120 ft. lbs.}{7 ft.} \) = \( \frac{240 ft. lbs.}{7 ft.} \) = 34.29 lbs.