ASVAB Mechanical Comprehension Practice Test 582069 Results

Your Results Global Average
Questions 5 5
Correct 0 3.44
Score 0% 69%

Review

1

Potential energy is energy that has the potential to be converted into what?

80% Answer Correctly

power

heat

 kinetic energy

work
Solution

Potential energy is the energy of an object by virtue of its position relative to other objects. It is energy that has the potential to be converted into kinetic energy.

2 How much resistance could a 65 lb. effort force lift using a block and tackle pulley that has 4 ropes supporting the resistance?
81% Answer Correctly
260 lbs.
390 lbs.
286 lbs.
251 lbs.
Solution

The mechanical advantage (MA) of a block and tackle pulley is equal to the number of times the effort force changes direction. An easy way to count how many times the effort force changes direction is to count the number of ropes that support the resistance which, in this problem, is 4. With a MA of 4, a 65 lbs. effort force could lift 65 lbs. x 4 = 260 lbs. resistance.

3 What is the mechanical advantage of this inclined plane if the length of the ramp is 35 ft. and the height of the green box is 7 ft.?
82% Answer Correctly
8
15
5
2
Solution

The mechanical advantage (MA) of an inclined plane is the effort distance divided by the resistance distance. In this case, the effort distance is the length of the ramp and the resistance distance is the height of the green box:

MA = \( \frac{d_e}{d_r} \) = \( \frac{35 ft.}{7 ft.} \) = 5

4 If the handles of a wheelbarrow are 2.5 ft. from the wheel axle, how many pounds of force must you exert to lift the handles if it's carrying a 140 lbs. load concentrated at a point 0.5 ft. from the axle?
52% Answer Correctly
-90.4
28
700
34.9
Solution
This problem describes a second-class lever and, for a second class lever, the effort force multiplied by the effort distance equals the resistance force multipied by the resistance distance: Fede = Frdr. In this problem we're looking for effort force:
\( F_e = \frac{F_r d_r}{d_e} \)
\( F_e = \frac{140 \times 0.5}{2.5} \)
\( F_e = \frac{70.0}{2.5} \)
\( F_e = 28 \)
5 If this lever is in equilibrium with an effort force of 10.0 ft. lb. at the blue arrow and a resistance force of 8 ft. lb. at the green box, what is its mechanical advantage?
48% Answer Correctly
0.8
3.8
1.2
0.72
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 = \( \frac{F_r}{F_e} \) = \( \frac{8 ft.}{10.0 ft.} \) = 0.8

In this case, the mechanical advantage is less than one meaning that each unit of effort force results in just 0.8 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.