ASVAB Mechanical Comprehension Practice Test 987737 Results

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

Review

1 If A = 12 ft., B = 2 ft., C = 7 ft., the green box weighs 40 lbs. and the blue box weighs 55 lbs., what does the orange box have to weigh for this lever to balance?

44% Answer Correctly

	52.86 lbs.
	20 lbs.
	17.62 lbs.
	0 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 12 ft. = 55 lbs. x 2 ft. + f_C x 7 ft.

480 ft. lbs. = 110 ft. lbs. + f_C x 7 ft.

f_C = \( \frac{480 ft. lbs. - 110 ft. lbs.}{7 ft.} \) = \( \frac{370 ft. lbs.}{7 ft.} \) = 52.86 lbs.

The mechanical advantage of a third class lever is always:

37% Answer Correctly

	not equal to one
	greater than one
	less than one
	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.

3 If this lever is in equilibrium with an effort force of 8.75 ft. lb. at the blue arrow and a resistance force of 7 ft. lb. at the green box, what is its mechanical advantage?

48% Answer Correctly

	3.8
	2.4
	2.8
	0.8

Solution

Mechanical advantage (MA) is the ratio by which effort force relates to resistance force. If both forces are known, calculating MA is simply a matter of dividing resistance force by effort force:

MA = \( \frac{F_r}{F_e} \) = \( \frac{7 ft.}{8.75 ft.} \) = 0.8

In this case, the mechanical advantage is less than one meaning that each unit of effort force results in just 0.8 units of resistance force. However, a third class lever like this isn't designed to multiply force like a first class lever. A third class lever is designed to multiply distance and speed at the resistance by sacrificing force at the resistance. Different lever styles have different purposes and multiply forces in different ways.

What type of load varies with time or affects a structure that experiences a high degree of movement?

66% Answer Correctly

	impact load
	dynamic load
	static load
	concentrated 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.

When all forces acting on a system cancel each other out, this is called:

80% Answer Correctly

	rest
	potential energy
	stasis
	equilibrium

Solution

When a system is stable or balanced (equilibrium) all forces acting on the system cancel each other out. In the case of torque, equilibrium means that the sum of the anticlockwise moments about a center of rotation equal the sum of the clockwise moments.