ASVAB Mechanical Comprehension Practice Test 13773 Results

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

Review

1 If the radius of the axle is 5 and the radius of the wheel is 6, what is the mechanical advantage of this wheel and axle configuration?

36% Answer Correctly

	1
	6
	-1
	1

Solution

The mechanical advantage of a wheel and axle lies in the difference in radius between the inner (axle) wheel and the outer wheel. But, this mechanical advantage is only realized when the input effort and load are applied to different wheels. Applying both input effort and load to the same wheel results in a mechanical advantage of 1.

Which class of lever is used to increase force on an object in the same direction as the force is applied?

53% Answer Correctly

	all of these
	third
	second
	first

Solution

A second-class lever is used to increase force on an object in the same direction as the force is applied. This lever requires a smaller force to lift a larger load but the force must be applied over a greater distance. The fulcrum is placed at one end of the lever and mechanical advantage increases as the object being lifted is moved closer to the fulcrum or the length of the lever is increased. An example of a second-class lever is a wheelbarrow.

3 If A = 10 ft., B = 1 ft., C = 6 ft., the green box weighs 40 lbs. and the blue box weighs 45 lbs., what does the orange box have to weigh for this lever to balance?

43% Answer Correctly

	59.17 lbs.
	40 lbs.
	4 lbs.
	29.58 lbs.

Solution

In order for this lever to balance, the torque acting on each side of the fulrum must be equal. So, the torque produced by A must equal the torque produced by B and C. Torque is weight x distance from the fulcrum which means that the following must be true for the lever to balance:

f_Ad_A = f_Bd_B + f_Cd_C

For this problem, this equation becomes:

40 lbs. x 10 ft. = 45 lbs. x 1 ft. + f_C x 6 ft.

400 ft. lbs. = 45 ft. lbs. + f_C x 6 ft.

f_C = \( \frac{400 ft. lbs. - 45 ft. lbs.}{6 ft.} \) = \( \frac{355 ft. lbs.}{6 ft.} \) = 59.17 lbs.

4 What is the efficiency of a machine has work input of 65 ft⋅lb and work output of 16 ft⋅lb?

67% Answer Correctly

	12%
	6%
	25%
	0%

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:
\( Efficiency = \frac{Work_{out}}{Work_{in}} \times 100 \) \( = \frac{16 ft⋅lb}{65 ft⋅lb} \times 100 \) \( = 25% \) %

Which of the following surfaces would have the highest coefficient of friction?

77% Answer Correctly

	steel
	ice
	marble
	concrete

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.