ASVAB Mechanical Comprehension Practice Test 268276 Results

	Your Results	Global Average
Questions	5	5
Correct	0	3.29
Score	0%	66%

Review

1 If you lift a 12 lbs. rock 44 ft. from the ground, how much work have you done?

71% Answer Correctly

	528 ft⋅lb
	3 ft⋅lb
	-32 ft⋅lb
	1056 ft⋅lb

Solution

Work is force times distance. In this case, the force is the weight of the rock so:
\( W = F \times d \)
\( W = 12 \times 44 \)
\( W = 528 \)

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

54% Answer Correctly

	coefficient of friction
	kinetic friction
	static friction
	normal 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.

What type of load is sudden and for a relatively short duration?

70% Answer Correctly

	concentrated load
	non-uniformly distributed load
	impact load
	dynamic load

Solution

A concentrated load acts on a relatively small area of a structure, a static uniformly distributed load doesn't create specific stress points or vary with time, a dynamic load varies with time or affects a structure that experiences a high degree of movement, an impact load is sudden and for a relatively short duration and a non-uniformly distributed load creates different stresses at different locations on a structure.

A block and tackle with four pulleys would have a mechanical advantage of:

79% Answer Correctly

	0
	4
	1
	2

Solution

Two or more pulleys used together constitute a block and tackle which, unlike a fixed pulley, does impart mechanical advantage as a function of the number of pulleys that make up the arrangement. So, for example, a block and tackle with three pulleys would have a mechanical advantage of three.

5 If the force applied at the blue arrow over 7 ft. moves the green box 1.4 ft., what is the mechanical advantage of this lever?

56% Answer Correctly

	15
	10
	7.5
	5

Solution

Mechanical advantage (MA) can be calculated knowing only the distance the effort (blue arrow) moves and the distance the resistance (green box) moves. The equation is:

MA = \( \frac{E_d}{R_d} \)

where E_d is the effort distance and R_d is the resistance distance. For this problem, the equation becomes:

MA = \( \frac{7 ft.}{1.4 ft.} \) = 5

You might be wondering how having an effort distance of 5 times the resistance distance is an advantage. Remember the principle of moments. For a lever in equilibrium the effort torque equals the resistance torque. Because torque is force x distance, if the effort distance is 5 times the resistance distance, the effort force must be \( \frac{1}{5} \) the resistance force. You're trading moving 5 times the distance for only having to use \( \frac{1}{5} \) the force.