ASVAB Mechanical Comprehension Practice Test 206438 Results

Your Results Global Average
Questions 5 5
Correct 0 3.62
Score 0% 72%

Review

1 If the green box weighs 65 lbs. and is 2 ft. from the fulcrum, how much force would need to be applied at the blue arrow to balance the lever if the arrow's distance from the fulcrum is 6 ft.?
62% Answer Correctly
86.67 lbs.
390 lbs.
21.67 lbs.
5.42 lbs.
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 Rb, our missing value, and plugging in our variables yields:

Rb = \( \frac{R_ad_a}{d_b} \) = \( \frac{65 lbs. \times 2 ft.}{6 ft.} \) = \( \frac{130 ft⋅lb}{6 ft.} \) = 21.67 lbs.

2 What is the efficiency of a machine has work input of 215 ft⋅lb and work output of 107 ft⋅lb?
67% Answer Correctly
2%
50%
0%
100%
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:
\( Efficiency = \frac{Work_{out}}{Work_{in}} \times 100 \) \( = \frac{107 ft⋅lb}{215 ft⋅lb} \times 100 \) \( = 50% \) %
3 70 lbs. of effort is used by a machine to lift a 280 lbs. box. What is the mechanical advantage of the machine?
84% Answer Correctly
4
3.6
4.4
5.5
Solution

Mechanical advantage is resistance force divided by effort force:

MA = \( \frac{F_r}{F_e} \) = \( \frac{280 lbs.}{70 lbs.} \) = 4

4

One Horsepower (hp) is equal to how many watts?

76% Answer Correctly

9.8

1

746

1492
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.

5

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

73% Answer Correctly

number of teeth

speed

diameter

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.