ASVAB Mechanical Comprehension Practice Test 972753 Results

Your Results Global Average
Questions 5 5
Correct 0 3.49
Score 0% 70%

Review

1 If you lift a 31 lbs. rock 47 ft. from the ground, how much work have you done?
71% Answer Correctly
1457 ft⋅lb
78 ft⋅lb
0 ft⋅lb
2914 ft⋅lb
Solution
Work is force times distance. In this case, the force is the weight of the rock so:
\( W = F \times d \)
\( W = 31 \times 47 \)
\( W = 1457 \)
2

The force required to initally get an object moving is __________ the force required to keep it moving. 

76% Answer Correctly

the same as

higher than

opposite

lower 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).

3 If the green arrow in this diagram represents 390 ft⋅lb of work, how far will the box move if it weighs 130 pounds?
73% Answer Correctly
520 ft.
12 ft.
3 ft.
0 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 390 ft⋅lb and the resistance force is 130 lbs. and we need to calculate the resistance distance:

Win = Fresistance x dresistance
390 ft⋅lb = 130 lbs. x dresistance
dresistance = \( \frac{390ft⋅lb}{130 lbs.} \) = 3 ft.

4

According to Boyle's law, for a fixed amount of gas kept at a fixed temperature, which of the following are inversely proportional?

63% Answer Correctly

pressure, volume

density, volume

pressure, density

volume, mass
Solution

Boyle's law states that "for a fixed amount of an ideal gas kept at a fixed temperature, pressure and volume are inversely proportional".

5 What is the efficiency of a machine has work input of 125 ft⋅lb and work output of 112 ft⋅lb?
67% Answer Correctly
22%
1%
90%
0%
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:
\( Efficiency = \frac{Work_{out}}{Work_{in}} \times 100 \) \( = \frac{112 ft⋅lb}{125 ft⋅lb} \times 100 \) \( = 90% \) %