ASVAB Mechanical Comprehension Practice Test 452854 Results

	Your Results	Global Average
Questions	5	5
Correct	0	3.21
Score	0%	64%

Review

1 What is the efficiency of a machine has work input of 115 ft⋅lb and work output of 40 ft⋅lb?

67% Answer Correctly

	8%
	70%
	2%
	35%

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:
\( Efficiency = \frac{Work_{out}}{Work_{in}} \times 100 \) \( = \frac{40 ft⋅lb}{115 ft⋅lb} \times 100 \) \( = 35% \) %

Drag is a type of:

81% Answer Correctly

	potential energy
	friction
	kinetic energy
	work

Solution

Drag is friction that opposes movement through a fluid like liquid or air. The amount of drag depends on the shape and speed of the object with slower objects experiencing less drag than faster objects and more aerodynamic objects experiencing less drag than those with a large leading surface area.

Which of the following will increase the mechanical advantage of this inclined plane?

59% Answer Correctly

	lower the force acting at the blue arrow
	lengthen the ramp
	shorten the ramp
	increase the force acting at the blue arrow

Solution

The mechanical advantage (MA) of an inclined plane is the effort distance divided by the resistance distance. In order to increase mechanical advantage, this ratio must increase which means making the effort distance longer and this can be accomplished by lengthening the length of the ramp.

4 If a 35 lbs. weight is placed 1 ft. from the fulcrum at the blue arrow and the green box is 6 ft. from the fulcrum, how much would the green box have to weigh to balance the lever?

61% Answer Correctly

	23.33 lbs.
	1.46 lbs.
	11.67 lbs.
	5.83 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 = \( \frac{R_bd_b}{d_a} \) = \( \frac{35 lbs. \times 1 ft.}{6 ft.} \) = \( \frac{35 ft⋅lb}{6 ft.} \) = 5.83 lbs.

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

53% Answer Correctly

	normal friction
	kinetic friction
	static friction
	coefficient of 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.