ASVAB Mechanical Comprehension Practice Test 500918 Results

Your Results Global Average
Questions 5 5
Correct 0 3.14
Score 0% 63%

Review

1

On Earth, acceleration due to gravity (g) is approximately __________. 

81% Answer Correctly

1 m/s

6.67 x 10-11 m/s2

9.8 m/s2

1 m/s2
Solution

Newton's Law of Univeral Gravitation defines the general formula for the attraction of gravity between two objects:  \(\vec{F_{g}} = { Gm_{1}m_{2} \over r^2}\) . In the specific case of an object falling toward Earth, the acceleration due to gravity (g) is approximately 9.8 m/s2. 

2

Which of these is the formula for kinetic energy?

68% Answer Correctly

\(KE = {1 \over 2}mv^2\)

\(KE = {1 \over 2}mh^2\)

\(KE = {m \over v^2 }\)

\(KE = mgh\)
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.

3 If the green box weighs 65 lbs. and 50 lbs. of force is applied 9 ft. from the fulcrum at the blue arrow, how far from the fulcrum would the green box need to be placed to balance the lever?
55% Answer Correctly
6.92 ft.
27.69 ft.
20.77 ft.
2.31 ft.
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 da, our missing value, and plugging in our variables yields:

da = \( \frac{R_bd_b}{R_a} \) = \( \frac{50 lbs. \times 9 ft.}{65 lbs.} \) = \( \frac{450 ft⋅lb}{65 lbs.} \) = 6.92 ft.

4 If this lever is in equilibrium with an effort force of 6.67 ft. lb. at the blue arrow and a resistance force of 4 ft. lb. at the green box, what is its mechanical advantage?
48% Answer Correctly
1.2
0.66
0.6
0.54
Solution

Mechanical advantage (MA) is the ratio by which effort force relates to resistance force. If both forces are known, calculating MA is simply a matter of dividing resistance force by effort force:

MA = \( \frac{F_r}{F_e} \) = \( \frac{4 ft.}{6.67 ft.} \) = 0.6

In this case, the mechanical advantage is less than one meaning that each unit of effort force results in just 0.6 units of resistance force. However, a third class lever like this isn't designed to multiply force like a first class lever. A third class lever is designed to multiply distance and speed at the resistance by sacrificing force at the resistance. Different lever styles have different purposes and multiply forces in different ways.

5

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

54% Answer Correctly

its direction

its weight

its mass

its speed
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.