ASVAB Mechanical Comprehension Practice Test 67483 Results

	Your Results	Global Average
Questions	5	5
Correct	0	2.98
Score	0%	60%

Review

1 What is the efficiency of a machine has work input of 85 ft⋅lb and work output of 68 ft⋅lb?

67% Answer Correctly

	160%
	1%
	80%
	320%

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:
\( Efficiency = \frac{Work_{out}}{Work_{in}} \times 100 \) \( = \frac{68 ft⋅lb}{85 ft⋅lb} \times 100 \) \( = 80% \) %

Which of these is the formula for kinetic energy?

67% Answer Correctly

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

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 will increase the mechanical advantage of this inclined plane?

59% Answer Correctly

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

Assuming force applied remains constant, which of the following will result in more work being done?

53% Answer Correctly

	moving the object with more acceleration
	moving the object farther
	increasing the coefficient of friction
	moving the object with more speed

Solution

Work is accomplished when force is applied to an object: W = Fd where F is force in newtons (N) and d is distance in meters (m). Thus, the more force that must be applied to move an object, the more work is done and the farther an object is moved by exerting force, the more work is done.

A fixed pulley is useful for which of the following?

53% Answer Correctly

	multiplying the input force
	changing the direction of the output force
	multiplying the input distance
	changing the direction of the input force

Solution

A fixed pulley is used to change the direction of a force and does not multiply the force applied. As such, it has a mechanical advantage of one. The benefit of a fixed pulley is that it can allow the force to be applied at a more convenient angle, for example, pulling downward or horizontally to lift an object instead of upward.