ASVAB Mechanical Comprehension Practice Test 602481 Results

Your Results Global Average
Questions 5 5
Correct 0 3.15
Score 0% 63%

Review

1

Two gears are connected and the smaller gear drives the larger gear. The speed of rotation will __________ and the torque will __________.

61% Answer Correctly

decrease, increase

increase, increase

decrease, decrease

increase, decrease
Solution

Connected gears of different numbers of teeth are used together to change the rotational speed and torque of the input force. If the smaller gear drives the larger gear, the speed of rotation will be reduced and the torque will increase. If the larger gear drives the smaller gear, the speed of rotation will increase and the torque will be reduced.

2 A = 5 ft., the green box weighs 40 lbs., and the blue box weighs 85 lbs. What does distance B need to be for this lever to balance?
65% Answer Correctly
2.35 ft.
0.78 ft.
200 ft.
8 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:

fAdA = fBdB

For this problem, the equation becomes:

40 lbs. x 5 ft. = 85 lbs. x dB

dB = \( \frac{40 \times 5 ft⋅lb}{85 lbs.} \) = \( \frac{200 ft⋅lb}{85 lbs.} \) = 2.35 ft.

3 If you have a gear train with two gears, the first with 28 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
3.8
2.3
4.3
3.5
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 = \( \frac{N_1}{N_2} \) = \( \frac{28}{12} \) = 2.3

4

The mechanical advantage of a wheel and axle is equal to the:

60% Answer Correctly

length of the axle

ratio of the diameters of the wheels

difference in the diameters of the wheels

difference in the lengths of the axles
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.

5

Which class of lever is used to increase force on an object in the same direction as the force is applied?

52% Answer Correctly

third

all of these

second

first
Solution

A second-class lever is used to increase force on an object in the same direction as the force is applied. This lever requires a smaller force to lift a larger load but the force must be applied over a greater distance. The fulcrum is placed at one end of the lever and mechanical advantage increases as the object being lifted is moved closer to the fulcrum or the length of the lever is increased. An example of a second-class lever is a wheelbarrow.