ASVAB Mechanical Comprehension Practice Test 43474 Results

Your Results Global Average
Questions 5 5
Correct 0 3.00
Score 0% 60%

Review

1

For any given surface, the coefficient of static friction is ___________ the coefficient of kinetic friction.

54% Answer Correctly

lower than

opposite

equal to

higher than
Solution

For any given surface, the coefficient of static friction is higher than the coefficient of kinetic friction. More force is required to initally get an object moving than is required to keep it moving. Additionally, static friction only arises in response to an attempt to move an object (overcome the normal force between it and the surface).

2 What is the efficiency of a machine has work input of 215 ft⋅lb and work output of 118 ft⋅lb?
67% Answer Correctly
110%
0%
45%
55%
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:
\( Efficiency = \frac{Work_{out}}{Work_{in}} \times 100 \) \( = \frac{118 ft⋅lb}{215 ft⋅lb} \times 100 \) \( = 55% \) %
3 If the green arrow in this diagram represents 800 ft⋅lb of work, how far will the box move if it weighs 200 pounds?
72% Answer Correctly
4 ft.
16 ft.
100 ft.
8 ft.
Solution
The Law of Work states that the work put into a machine is equal to the work received from the machine under ideal conditions. In equation form, that's:

Win = Wout
Feffort x deffort = Fresistance x dresistance

In this problem, the effort work is 800 ft⋅lb and the resistance force is 200 lbs. and we need to calculate the resistance distance:

Win = Fresistance x dresistance
800 ft⋅lb = 200 lbs. x dresistance
dresistance = \( \frac{800ft⋅lb}{200 lbs.} \) = 4 ft.

4

Which of the following will increase the mechanical advantage of this inclined plane?

59% Answer Correctly

lower the force acting at the blue arrow

lengthen the ramp

increase the force acting at the blue arrow

shorten the ramp
Solution

The mechanical advantage (MA) of an inclined plane is the effort distance divided by the resistance distance. In order to increase mechanical advantage, this ratio must increase which means making the effort distance longer and this can be accomplished by lengthening the length of the ramp.

5

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

50% Answer Correctly

wheel and axle

first-class lever

block and tackle

inclined plane
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.