ASVAB Mechanical Comprehension Practice Test 591252 Results

Your Results Global Average
Questions 5 5
Correct 0 3.07
Score 0% 61%

Review

1 If the green box weighs 10 lbs. and 40 lbs. of force is applied 3 ft. from the fulcrum at the blue arrow, how far from the fulcrum would the green box need to be placed to balance the lever?
55% Answer Correctly
48 ft.
12 ft.
0 ft.
24 ft.
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:

Rada = Rbdb

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 da, our missing value, and plugging in our variables yields:

da = \( \frac{R_bd_b}{R_a} \) = \( \frac{40 lbs. \times 3 ft.}{10 lbs.} \) = \( \frac{120 ft⋅lb}{10 lbs.} \) = 12 ft.

2

Which of the following is not a type of structural load?

49% Answer Correctly

live load

occupancy load

dead load

wind load
Solution

Dead load is the weight of the building and materials, live load is additional weight due to occupancy or use, snow load is the weight of accumulated snow on a structure and wind load is the force of wind pressures against structure surfaces.

3

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

89% Answer Correctly

fixed pulley

wheel and axle

first-class lever

block and tackle
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.

4 If a 15 lbs. weight is placed 3 ft. from the fulcrum at the blue arrow and the green box is 2 ft. from the fulcrum, how much would the green box have to weigh to balance the lever?
61% Answer Correctly
22.5 lbs.
90 lbs.
5.63 lbs.
7.5 lbs.
Solution

To balance this lever the torques on each side of the fulcrum must be equal. Torque is weight x distance from the fulcrum so the equation for equilibrium is:

Rada = Rbdb

where a represents the left side of the fulcrum and b the right, R is resistance (weight) and d is the distance from the fulcrum.

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

Ra = \( \frac{R_bd_b}{d_a} \) = \( \frac{15 lbs. \times 3 ft.}{2 ft.} \) = \( \frac{45 ft⋅lb}{2 ft.} \) = 22.5 lbs.

5

Which of the following is not true of a  first-class lever?

51% Answer Correctly

increases force

changes the direction of force

increases distance

decreases distance
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.