ASVAB Mechanical Comprehension Practice Test 639625 Results

	Your Results	Global Average
Questions	5	5
Correct	0	2.63
Score	0%	53%

Review

The principle of conservation of mechanical energy states that, as long as no other forces are applied, what will remain constant as an object falls?

45% Answer Correctly

	total mechanical energy
	kinetic energy
	acceleration
	potential energy

Solution

As an object falls, its potential energy is converted into kinetic energy. The principle of conservation of mechanical energy states that, as long as no other forces are applied, total mechanical energy (PE + KE) of the object will remain constant at all points in its descent.

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

61% Answer Correctly

	low corrosive action
	chemically stable
	high melting point
	low density

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.

Force of friction due to kinetic friction is __________ the force of friction due to static friction.

40% Answer Correctly

	higher than
	the same as
	lower than
	opposite

Solution

The formula for force of friction (F_f) is the same whether kinetic or static friction applies: F_{f =}μF_N. To distinguish between kinetic and static friction, μ_k and μ_s are often used in place of μ.

4 A 280 lb. barrel is rolled up a 5 ft. ramp to a platform that's 5 ft. tall. What effort is required to move the barrel?

53% Answer Correctly

	277 lbs.
	420 lbs.
	280 lbs.
	840 lbs.

Solution

This problem describes an inclined plane and, for an inclined plane, the effort force multiplied by the effort distance equals the resistance force multipied by the resistance distance:

F_ed_e = F_rd_r

Plugging in the variables from this problem yields:

F_e x 5 ft. = 280 lbs. x 5 ft.
F_e = \( \frac{1400 ft⋅lb}{5 ft.} \) = 280 lbs.

5 What is the efficiency of a machine has work input of 155 ft⋅lb and work output of 85 ft⋅lb?

67% Answer Correctly

	55%
	110%
	1%
	220%

Solution

Due to friction, a machine will never be able to utilize 100% of its work input. A certain percentage of that input will be lost in overcoming friction within the machine. Effeciency is a measure of how much of a machine's work input can be turned into useful work output and is calculated by dividing work output by work input and multiplying the result by 100:
\( Efficiency = \frac{Work_{out}}{Work_{in}} \times 100 \) \( = \frac{85 ft⋅lb}{155 ft⋅lb} \times 100 \) \( = 55% \) %