ASVAB Mechanical Comprehension Practice Test 480039 Results

	Your Results	Global Average
Questions	5	5
Correct	0	3.55
Score	0%	71%

Review

1 If input effort is 300 ft⋅lb, what output effort will be produced by a machine with a mechanical advantage of 3?

79% Answer Correctly

	450ft⋅lb
	900 ft⋅lb
	3600ft⋅lb
	1800ft⋅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 3 will multiply an input effort of 300 ft⋅lb by 3 to produce an output effort of 900 ft⋅lb.

2 If 15 lbs. of force is applied 6 ft. from the fulcrum at the blue arrow and the green box is 4 ft. from the fulcrum, how much would the green box have to weigh to balance the lever?

62% Answer Correctly

	90 lbs.
	7.5 lbs.
	22.5 lbs.
	2 lbs.

Solution

To balance this lever the torques at the green box and the blue arrow must be equal. Torque is weight x distance from the fulcrum so the equation for equilibrium is:

R_ad_a = R_bd_b

where a represents the green box and b the blue arrow, R is resistance (weight/force) and d is the distance from the fulcrum.

Solving for R_a, our missing value, and plugging in our variables yields:

R_a = \( \frac{R_bd_b}{d_a} \) = \( \frac{15 lbs. \times 6 ft.}{4 ft.} \) = \( \frac{90 ft⋅lb}{4 ft.} \) = 22.5 lbs.

3 If you have a gear train with two gears, the first with 36 teeth and the second with 12 teeth, how many revolutions does the second gear make for each revolution of the first gear?

77% Answer Correctly

	3
	1.5
	5
	-4

Solution

The gear ratio (V_r) of a gear train 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 only two gears so the equation becomes:

V_r = \( \frac{N_1}{N_2} \) = \( \frac{36}{12} \) = 3

4 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

	2.4
	0.8
	2.8
	3.8

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.

The steering wheel of a car is an example of which type of simple machine?

88% Answer Correctly

	wheel and axle
	block and tackle
	first-class lever
	fixed pulley

Solution

A wheel and axle uses two different diameter wheels mounted to a connecting axle. Force is applied to the larger wheel and large movements of this wheel result in small movements in the smaller wheel. Because a larger movement distance is being translated to a smaller distance, force is increased with a mechanical advantage equal to the ratio of the diameters of the wheels. An example of a wheel and axle is the steering wheel of a car.