ASVAB Mechanical Comprehension Practice Test 472687 Results

	Your Results	Global Average
Questions	5	5
Correct	0	2.79
Score	0%	56%

Review

Which of these is the formula for kinetic energy?

67% Answer Correctly

	\(KE = mgh\)
	\(KE = {1 \over 2}mv^2\)
	\(KE = {1 \over 2}mh^2\)
	\(KE = {m \over v^2 }\)

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.

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

53% Answer Correctly

	coefficient of friction
	normal friction
	static friction
	kinetic 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.

The mechanical advantage of a third class lever is always:

37% Answer Correctly

	not equal to one
	less than one
	greater than one
	equal to 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 What is the power output of a 4 hp engine that's 60% efficient?

40% Answer Correctly

	240 \( \frac{ft⋅lb}{s} \)
	1320 \( \frac{ft⋅lb}{s} \)
	660 \( \frac{ft⋅lb}{s} \)
	5280 \( \frac{ft⋅lb}{s} \)

Solution

\( Efficiency = \frac{Power_{out}}{Power_{in}} \times 100 \)
Solving for power out: \( P_{o} = \frac{E \times P_{i}}{100} \)
Knowing that 1 hp = 550 \( \frac{ft⋅lb}{s} \), P_i becomes 4 hp x 550 \( \frac{ft⋅lb}{s} \) = 2200 \( \frac{ft⋅lb}{s} \)
\( P_{o} = \frac{E \times P_{i}}{100} = \frac{60 \times 2200 \frac{ft⋅lb}{s}}{100} \) \( = \frac{132000 \frac{ft⋅lb}{s}}{100} \) = 1320 \( \frac{ft⋅lb}{s} \)

5 What is the mechanical advantage of this inclined plane if the length of the ramp is 40 ft. and the height of the green box is 8 ft.?

82% Answer Correctly

	6.5
	8
	7.5
	5

Solution

The mechanical advantage (MA) of an inclined plane is the effort distance divided by the resistance distance. In this case, the effort distance is the length of the ramp and the resistance distance is the height of the green box:

MA = \( \frac{d_e}{d_r} \) = \( \frac{40 ft.}{8 ft.} \) = 5