ASVAB Mechanical Comprehension Practice Test 72174 Results

Your Results Global Average
Questions 5 5
Correct 0 3.22
Score 0% 64%

Review

1

Which of the following represents how much two materials resist sliding across each other?

53% Answer Correctly

normal friction

coefficient of friction

kinetic friction

static friction
Solution

Coefficient of friction (μ) represents how much two materials resist sliding across each other.  Smooth surfaces like ice have low coefficients of friction while rough surfaces like concrete have high μ.

2 What is the efficiency of a machine has work input of 75 ft⋅lb and work output of 52 ft⋅lb?
67% Answer Correctly
280%
70%
1%
35%
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:
\( Efficiency = \frac{Work_{out}}{Work_{in}} \times 100 \) \( = \frac{52 ft⋅lb}{75 ft⋅lb} \times 100 \) \( = 70% \) %
3

A watt is the unit for which of the following?

71% Answer Correctly

energy

mechanical advantage

work

power
Solution

Power is the rate at which work is done, P = w/t, or work per unit time. The watt (W) is the unit for power and is equal to 1 joule (or newton-meter) per second. Horsepower (hp) is another familiar unit of power used primarily for rating internal combustion engines. 1 hp equals 746 watts.

4

Potential energy is energy that has the potential to be converted into what?

80% Answer Correctly

power

work

 kinetic energy

heat
Solution

Potential energy is the energy of an object by virtue of its position relative to other objects. It is energy that has the potential to be converted into kinetic energy.

5 How much work can a 7 hp engine do in 5 seconds?
52% Answer Correctly
0 ft⋅lb
19250 ft⋅lb
14 ft⋅lb
3 ft⋅lb
Solution
Horsepower (hp) is a common measure of power output for complex machines. By definition, a 1 hp machine does 550 ft⋅lb of work in 1 second: 1 hp = 550 ft⋅lb/s. Substituting the variables for this problem gives us:
\( W = 7 hp \times 550 \frac{ft⋅lb}{s} \times 5s = 19250 ft⋅lb \)