ASVAB Mechanical Comprehension Practice Test 786615 Results

	Your Results	Global Average
Questions	5	5
Correct	0	2.69
Score	0%	54%

Review

1 If the green box weighs 50 lbs. and is 4 ft. from the fulcrum, how much force would need to be applied at the blue arrow to balance the lever if the arrow's distance from the fulcrum is 7 ft.?

62% Answer Correctly

	28.57 lbs.
	0 lbs.
	114.29 lbs.
	14.29 lbs.

Solution

To balance this lever the torques at the green box and the blue arrow 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 green box and b the blue arrow, R is resistance (weight/force) and d is the distance from the fulcrum.

Solving for R_b, our missing value, and plugging in our variables yields:

R_b = \( \frac{R_ad_a}{d_b} \) = \( \frac{50 lbs. \times 4 ft.}{7 ft.} \) = \( \frac{200 ft⋅lb}{7 ft.} \) = 28.57 lbs.

For a hydraulic system, pressure applied to the input of the system will increase the pressure in which parts of the system?

58% Answer Correctly

	everywhere in the system
	the portions of the system at an altitude below the input
	the portions of the system at an altitude above the input
	all of these are correct

Solution

Pascal's law states that a pressure change occurring anywhere in a confined incompressible fluid is transmitted throughout the fluid such that the same change occurs everywhere. For a hydraulic system, this means that a pressure applied to the input of the system will increase the pressure everywhere in the system.

3 If this lever is in equilibrium with an effort force of 7.78 ft. lb. at the blue arrow and a resistance force of 7 ft. lb. at the green box, what is its mechanical advantage?

48% Answer Correctly

	2.4
	0.3
	0.9
	0.81

Solution

Mechanical advantage (MA) is the ratio by which effort force relates to resistance force. If both forces are known, calculating MA is simply a matter of dividing resistance force by effort force:

MA = \( \frac{F_r}{F_e} \) = \( \frac{7 ft.}{7.78 ft.} \) = 0.9

In this case, the mechanical advantage is less than one meaning that each unit of effort force results in just 0.9 units of resistance force. However, a third class lever like this isn't designed to multiply force like a first class lever. A third class lever is designed to multiply distance and speed at the resistance by sacrificing force at the resistance. Different lever styles have different purposes and multiply forces in different ways.

What's the last gear in a gear train called?

38% Answer Correctly

	idler gear
	driven gear
	output gear
	driver gear

Solution

A gear train is two or more gears linked together. Gear trains are designed to increase or reduce the speed or torque outpout of a rotating system or change the direction of its output. The first gear in the chain is called the driver and the last gear in the chain the driven gear with the gears between them called idler gears.

Which of these is the formula for kinetic energy?

68% Answer Correctly

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

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.