ASVAB Mechanical Comprehension Practice Test 560258 Results

Your Results Global Average
Questions 5 5
Correct 0 3.15
Score 0% 63%

Review

1

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

54% Answer Correctly

its speed

its mass

its weight

its direction
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

The mechanical advantage of a wheel and axle is equal to the:

61% Answer Correctly

difference in the lengths of the axles

ratio of the diameters of the wheels

length of the axle

difference in the diameters of the wheels
Solution

A wheel and axle uses two different diameter wheels mounted to a connecting axle. Force is applied to the larger wheel and large movements of this wheel result in small movements in the smaller wheel. Because a larger movement distance is being translated to a smaller distance, force is increased with a mechanical advantage equal to the ratio of the diameters of the wheels. An example of a wheel and axle is the steering wheel of a car.

3 If the green box weighs 50 lbs. and is 5 ft. from the fulcrum, how far from the fulcrum would a 15 lbs. weight need to be placed to balance the lever?
61% Answer Correctly
16.67 ft.
66.67 ft.
0 ft.
4.17 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 = \( \frac{R_ad_a}{R_b} \) = \( \frac{50 lbs. \times 5 ft.}{15 lbs.} \) = \( \frac{250 ft⋅lb}{15 lbs.} \) = 16.67 ft.

4 If the force applied at the blue arrow over 6 ft. moves the green box 1.0 ft., what is the mechanical advantage of this lever?
56% Answer Correctly
6.6
6
12
3
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 = \( \frac{6 ft.}{1.0 ft.} \) = 6

You might be wondering how having an effort distance of 6 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 6 times the resistance distance, the effort force must be \( \frac{1}{6} \) the resistance force. You're trading moving 6 times the distance for only having to use \( \frac{1}{6} \) the force.

5 50 lbs. of effort is used by a machine to lift a 100 lbs. box. What is the mechanical advantage of the machine?
84% Answer Correctly
2.2
2
3
4
Solution

Mechanical advantage is resistance force divided by effort force:

MA = \( \frac{F_r}{F_e} \) = \( \frac{100 lbs.}{50 lbs.} \) = 2