ASVAB Mechanical Comprehension Practice Test 668378 Results

Your Results Global Average
Questions 5 5
Correct 0 2.96
Score 0% 59%

Review

1

Which of the following is not true of a  first-class lever?

51% Answer Correctly

decreases distance

changes the direction of force

increases force

increases distance
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.

2 If the green box weighs 10 lbs. and is 3 ft. from the fulcrum, how far from the fulcrum would a 75 lbs. weight need to be placed to balance the lever?
61% Answer Correctly
1.6 ft.
0 ft.
0.4 ft.
0.2 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 db, our missing value, and plugging in our variables yields:

db = \( \frac{R_ad_a}{R_b} \) = \( \frac{10 lbs. \times 3 ft.}{75 lbs.} \) = \( \frac{30 ft⋅lb}{75 lbs.} \) = 0.4 ft.

3

Power is the rate at which:

62% Answer Correctly

work is done

input force is transferred to output force

friction is overcome

potential energy is converted into kinetic energy
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 How much work can a 9 hp engine do in 8 seconds?
52% Answer Correctly
18 ft⋅lb
1 ft⋅lb
0 ft⋅lb
39600 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:
\( W = 9 hp \times 550 \frac{ft⋅lb}{s} \times 8s = 39600 ft⋅lb \)
5

A watt is the unit for which of the following?

71% Answer Correctly

work

power

energy

mechanical advantage
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.