ASVAB Mechanical Comprehension Practice Test 699594 Results

	Your Results	Global Average
Questions	5	5
Correct	0	3.27
Score	0%	65%

Review

Two or more pulleys used together are called:

71% Answer Correctly

	wheel and axle
	third-class lever
	gears
	block and tackle

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.

Which of the following will increase the mechanical advantage of a second-class lever?

55% Answer Correctly

	move the object being lifted closer to the fulcrum
	decrease the length of the lever
	move the object being lifted farther away from the fulcrum
	move the fulcrum between the force and the object being lifted

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.

Lisa lifts a 25 pound box from the floor onto a loading dock 4 ft. off the ground. Sam slides the same box along a ramp to move it up another 4 ft. onto a flatbed truck. Who has done more work?

50% Answer Correctly

	Lisa
	Sam
	They have done an equal amount of work
	Neither have done any work

Solution

Work is force multiplied by distance. Because both Connie and Sam moved the same weight the same distance they have done an equal amount of work. Sam employed the mechnacial advantage of an inclined plane so he exerted less effort to do the work but the amount of work done was still the same.

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

85% Answer Correctly

	leather
	concrete
	ice
	tile

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.

5 A = 8 ft., the green box weighs 50 lbs., and the blue box weighs 75 lbs. What does distance B need to be for this lever to balance?

65% Answer Correctly

	5.33 ft.
	0 ft.
	10.67 ft.
	600 ft.

Solution

In order for this lever to balance, the torque acting on side A must equal the torque acting on side B. 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

For this problem, the equation becomes:

50 lbs. x 8 ft. = 75 lbs. x d_B

d_B = \( \frac{50 \times 8 ft⋅lb}{75 lbs.} \) = \( \frac{400 ft⋅lb}{75 lbs.} \) = 5.33 ft.