ASVAB Mechanical Comprehension Practice Test 63178 Results

Your Results Global Average
Questions 5 5
Correct 0 2.91
Score 0% 58%

Review

1

Which of these will have the most impact on the kinetic energy of an object?

54% Answer Correctly

its direction

its speed

its weight

its mass
Solution

Kinetic energy is the energy of movement and is a function of the mass of an object and its speed: \(KE = {1 \over 2}mv^2\) where m is mass in kilograms, v is speed in meters per second, and KE is in joules. The most impactful quantity to kinetic energy is velocity as an increase in mass increases KE linearly while an increase in speed increases KE exponentially.

2 If the green box weighs 20 lbs. and is 3 ft. from the fulcrum, how far from the fulcrum would a 40 lbs. weight need to be placed to balance the lever?
61% Answer Correctly
3 ft.
0 ft.
0.75 ft.
1.5 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 = \( \frac{R_ad_a}{R_b} \) = \( \frac{20 lbs. \times 3 ft.}{40 lbs.} \) = \( \frac{60 ft⋅lb}{40 lbs.} \) = 1.5 ft.

3 If the force applied at the blue arrow over 8 ft. moves the green box 1.6 ft., what is the mechanical advantage of this lever?
56% Answer Correctly
7.5
6
4.5
5
Solution

Mechanical advantage (MA) can be calculated knowing only the distance the effort (blue arrow) moves and the distance the resistance (green box) moves. The equation is:

MA = \( \frac{E_d}{R_d} \)

where Ed is the effort distance and Rd is the resistance distance. For this problem, the equation becomes:

MA = \( \frac{8 ft.}{1.6 ft.} \) = 5

You might be wondering how having an effort distance of 5 times the resistance distance is an advantage. Remember the principle of moments. For a lever in equilibrium the effort torque equals the resistance torque. Because torque is force x distance, if the effort distance is 5 times the resistance distance, the effort force must be \( \frac{1}{5} \) the resistance force. You're trading moving 5 times the distance for only having to use \( \frac{1}{5} \) the force.

4

Gear ratio indicates which of the following about two connected gears?

59% Answer Correctly

efficiency

work done

power conversion

mechanical advantage
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.

5 If the green box weighs 40 lbs. and is 4 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 5 ft.?
62% Answer Correctly
8 lbs.
0 lbs.
32 lbs.
10.67 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 = \( \frac{R_ad_a}{d_b} \) = \( \frac{40 lbs. \times 4 ft.}{5 ft.} \) = \( \frac{160 ft⋅lb}{5 ft.} \) = 32 lbs.