ASVAB Mechanical Comprehension Practice Test 28985 Results

	Your Results	Global Average
Questions	5	5
Correct	0	2.79
Score	0%	56%

Review

Depending on where you apply effort and resistance, the wheel and axle can multiply:

45% Answer Correctly

	force or distance
	power or distance
	speed or power
	force or speed

Solution

If you apply the resistance to the axle and the effort to the wheel, the wheel and axle will multiply force and if you apply the resistance to the wheel and the effort to the axle, it will multiply speed.

2 If this lever is in equilibrium with an effort force of 3.33 ft. lb. at the blue arrow and a resistance force of 2 ft. lb. at the green box, what is its mechanical advantage?

48% Answer Correctly

	0.54
	0.2
	0.6
	6.6

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 = \( \frac{F_r}{F_e} \) = \( \frac{2 ft.}{3.33 ft.} \) = 0.6

In this case, the mechanical advantage is less than one meaning that each unit of effort force results in just 0.6 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.

The science that deals with motion and the forces that produce motion is called which of the following?

57% Answer Correctly

	mechanics
	engineering
	physics
	aeronautics

Solution

Mechanics deals with motion and the forces that produce motion.

4 If you have a gear train with three gears, the first with 28 teeth, the second with 12 teeth, and the third with 6 teeth, what is its mechanical advantage?

50% Answer Correctly

	1.7
	4.7
	7.7
	6.2

Solution

The mechanical advantage of a gear train is its gear ratio. The gear ratio (V_r) is the product of the gear ratios between the pairs of meshed gears. Let N represent the number of teeth for each gear:

V_r = \( \frac{N_1}{N_2} \) \( \frac{N_2}{N_3} \) \( \frac{N_3}{N_4} \) ... \( \frac{N_n}{N_{n+1}} \)

In this problem, we have three gears so the equation becomes:

V_r = \( \frac{N_1}{N_2} \) \( \frac{N_2}{N_3} \) = \( \frac{28}{12} \) \( \frac{12}{6} \) = \( \frac{28}{6} \) = 4.7

5 If input effort is 200 ft⋅lb, what output effort will be produced by a machine with a mechanical advantage of 5?

79% Answer Correctly

	1000 ft⋅lb
	250ft⋅lb
	0ft⋅lb
	2000ft⋅lb

Solution

Mechanical advantage is the ratio of output force to input force and tells us by how many times a machine multiplies input effort. So, a machine with a mechanical advantage of 5 will multiply an input effort of 200 ft⋅lb by 5 to produce an output effort of 1000 ft⋅lb.