ASVAB Mechanical Comprehension Practice Test 844892 Results

	Your Results	Global Average
Questions	5	5
Correct	0	2.78
Score	0%	56%

Review

1 A = 7 ft., the green box weighs 30 lbs., and the blue box weighs 45 lbs. What does distance B need to be for this lever to balance?

65% Answer Correctly

	14 ft.
	4 ft.
	0 ft.
	4.67 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 7 ft. = 45 lbs. x d_B

d_B = \( \frac{30 \times 7 ft⋅lb}{45 lbs.} \) = \( \frac{210 ft⋅lb}{45 lbs.} \) = 4.67 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

	increase torque
	increase applied force
	decrease applied force
	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).

The mechanical advantage of a block and tackle is equal to which of the following?

69% Answer Correctly

	the number of input forces
	the number of loads
	the number of pulleys
	the number of connecting ropes

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 represents how much two materials resist sliding across each other?

53% Answer Correctly

	coefficient of friction
	kinetic friction
	normal friction
	static 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.

The mechanical advantage of a third class lever is always:

37% Answer Correctly

	greater than one
	less than one
	equal to 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.