ASVAB Mechanical Comprehension Practice Test 661576 Results

	Your Results	Global Average
Questions	5	5
Correct	0	3.30
Score	0%	66%

Review

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

77% Answer Correctly

	ice
	marble
	steel
	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.

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

79% Answer Correctly

	1
	0
	2
	4

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 fulcrum between the force and the object being lifted
	move the object being lifted farther away from the fulcrum

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.

4 A = 6 ft., the green box weighs 30 lbs., and the blue box weighs 50 lbs. What does distance B need to be for this lever to balance?

65% Answer Correctly

	180 ft.
	0.9 ft.
	3.6 ft.
	14.4 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:

30 lbs. x 6 ft. = 50 lbs. x d_B

d_B = \( \frac{30 \times 6 ft⋅lb}{50 lbs.} \) = \( \frac{180 ft⋅lb}{50 lbs.} \) = 3.6 ft.

Torque involves a perpendicular force applied to a lever arm that moves around a center of rotation. Increasing the length of the lever arm will do which of the following?

54% Answer Correctly

	decrease applied force
	increase applied force
	increase torque
	decrease torque

Solution

Torque measures force applied during rotation: τ = rF. Torque (τ, the Greek letter tau) = the radius of the lever arm (r) multiplied by the force (F) applied. Radius is measured from the center of rotation or fulcrum to the point at which the perpendicular force is being applied. The resulting unit for torque is newton-meter (N-m) or foot-pound (ft-lb).