ASVAB Mechanical Comprehension Practice Test 964770 Results

	Your Results	Global Average
Questions	5	5
Correct	0	3.28
Score	0%	66%

Review

The mechanical advantage of connected gears is proportional to which characteristic of the gears?

73% Answer Correctly

	number of teeth
	diameter
	circumference
	speed

Solution

The mechanical advantage (amount of change in speed or torque) of connected gears is proportional to the number of teeth each gear has. Called gear ratio, it's the ratio of the number of teeth on the larger gear to the number of teeth on the smaller gear. For example, a gear with 12 teeth connected to a gear with 9 teeth would have a gear ratio of 4:3.

Hydraulics is the transmission of force through the use of which of the following?

73% Answer Correctly

	liquids
	gear systems
	air pressure
	torque

Solution

Hydraulics is the transmission of force through the use of liquids. Liquids are especially suited for transferring force in complex machines because they compress very little and can occupy very small spaces. Hydraulic pressure is calculated by dividing force by the area over which it is applied: P = F/A where F is force in pounds, A is area in square inches, and the resulting pressure is in pounds per square inch (psi).

3 If A = 1 ft. and the green box weighs 30 lbs. what is the torque acting on the A side of this lever?

74% Answer Correctly

	120 ft⋅lb
	30 ft⋅lb
	90 ft⋅lb
	0 ft⋅lb

Solution

For a lever, torque is weight x distance from the fulcrum which, in this case, is: 30 ft. x 1 lbs. = 30 ft⋅lb

4 What is the efficiency of a machine has work input of 70 ft⋅lb and work output of 49 ft⋅lb?

67% Answer Correctly

	140%
	17%
	70%
	1%

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:
\( Efficiency = \frac{Work_{out}}{Work_{in}} \times 100 \) \( = \frac{49 ft⋅lb}{70 ft⋅lb} \times 100 \) \( = 70% \) %

The mechanical advantage of a third class lever is always:

37% Answer Correctly

	equal to one
	greater than one
	less than one
	not 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.