ASVAB Mechanical Comprehension Practice Test 202710 Results

Your Results Global Average
Questions 5 5
Correct 0 3.17
Score 0% 63%

Review

1

A truck is using a rope to pull a car. Tension in the rope is greatest in which of the following places?

50% Answer Correctly

in the middle

tension is equal in all parts of the rope

near the truck

near the car
Solution

Tension is a force that stretches or elongates something. When a cable or rope is used to pull an object, for example, it stretches internally as it accepts the weight that it's moving. Although tension is often treated as applying equally to all parts of a material, it's greater at the places where the material is under the most stress.

2

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

69% Answer Correctly

inclined plane

second-class lever

first-class lever

third-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.

3 What is the efficiency of a machine has work input of 125 ft⋅lb and work output of 43 ft⋅lb?
67% Answer Correctly
0%
70%
35%
140%
Solution
Due to friction, a machine will never be able to utilize 100% of its work input. A certain percentage of that input will be lost in overcoming friction within the machine. Effeciency is a measure of how much of a machine's work input can be turned into useful work output and is calculated by dividing work output by work input and multiplying the result by 100:
\( Efficiency = \frac{Work_{out}}{Work_{in}} \times 100 \) \( = \frac{43 ft⋅lb}{125 ft⋅lb} \times 100 \) \( = 35% \) %
4

The mechanical advantage of connected gears is proportional to which characteristic of the gears?

73% Answer Correctly

number of teeth

diameter

speed

circumference
Solution

The mechanical advantage (amount of change in speed or torque) of connected gears is proportional to the number of teeth each gear has. Called gear ratio, it's the ratio of the number of teeth on the larger gear to the number of teeth on the smaller gear.  For example, a gear with 12 teeth connected to a gear with 9 teeth would have a gear ratio of 4:3.

5 The green box weighs 15 lbs. and a 35 lbs. weight is placed 5 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?
57% Answer Correctly
11.67 ft.
2.92 ft.
75 ft.
3.89 ft.
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 da, our missing value, and plugging in our variables yields:

da = \( \frac{R_bd_b}{R_a} \) = \( \frac{35 lbs. \times 5 ft.}{15 lbs.} \) = \( \frac{175 ft⋅lb}{15 lbs.} \) = 11.67 ft.