ASVAB Mechanical Comprehension Practice Test 372837 Results

Your Results Global Average
Questions 5 5
Correct 0 3.44
Score 0% 69%

Review

1 If you have a gear train with two gears, the first with 24 teeth and the second with 12 teeth, how many revolutions does the second gear make for each revolution of the first gear?
78% Answer Correctly
-7
6
1.8
2
Solution

The gear ratio (Vr) 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:

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

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

Vr = \( \frac{N_1}{N_2} \) = \( \frac{24}{12} \) = 2

2

What defines the mechanical advantage of a first class lever?

65% Answer Correctly

output distance

input force

output force 

position of the fulcrum
Solution

A first-class lever is used to increase force or distance while changing the direction of the force. The lever pivots on a fulcrum and, when a force is applied to the lever at one side of the fulcrum, the other end moves in the opposite direction. The position of the fulcrum also defines the mechanical advantage of the lever. If the fulcrum is closer to the force being applied, the load can be moved a greater distance at the expense of requiring a greater input force. If the fulcrum is closer to the load, less force is required but the force must be applied over a longer distance. An example of a first-class lever is a seesaw / teeter-totter.

3

A a seesaw / teeter-totter is an example of which of the following?

69% Answer Correctly

inclined plane

third-class lever

first-class lever

second-class lever
Solution

A first-class lever is used to increase force or distance while changing the direction of the force. The lever pivots on a fulcrum and, when a force is applied to the lever at one side of the fulcrum, the other end moves in the opposite direction. The position of the fulcrum also defines the mechanical advantage of the lever. If the fulcrum is closer to the force being applied, the load can be moved a greater distance at the expense of requiring a greater input force. If the fulcrum is closer to the load, less force is required but the force must be applied over a longer distance. An example of a first-class lever is a seesaw / teeter-totter.

4 What's the mechanical advantage of a wedge that's 5 inches wide and 20 inches long?
83% Answer Correctly
1
4.4
4
-3
Solution

The mechanical advantage (MA) of a wedge is its length divided by its thickness:

MA = \( \frac{l}{t} \) = \( \frac{20 in.}{5 in.} \) = 4

5

A screw is most like which of the following other simple machines?

50% Answer Correctly

wheel and axle

block and tackle

inclined plane

first-class lever
Solution

A screw is an inclined plane wrapped in ridges (threads) around a cylinder. The distance between these ridges defines the pitch of the screw and this distance is how far the screw advances when it is turned once. The mechanical advantage of a screw is its circumference divided by the pitch.