ASVAB Mechanical Comprehension Practice Test 257589 Results

Your Results Global Average
Questions 5 5
Correct 0 2.93
Score 0% 59%

Review

1

Normal force is generally equal to the __________ of an object.

61% Answer Correctly

weight

mass

density

coefficient of friction
Solution

Normal force arises on a flat horizontal surface in response to an object's weight pressing it down. Consequently, normal force is generally equal to the object's weight.

2

What defines the mechanical advantage of a first class lever?

65% Answer Correctly

output distance

input force

position of the fulcrum

output force 
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.

3 If the green box weighs 20 lbs. and is 3 ft. from the fulcrum, how much weight would need to be placed at the blue arrow to balance the lever if the arrow's distance from the fulcrum is 6 ft.?
63% Answer Correctly
10 lbs.
2.5 lbs.
5 lbs.
30 lbs.
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 Rb, our missing value, and plugging in our variables yields:

Rb = \( \frac{R_ad_a}{d_b} \) = \( \frac{20 lbs. \times 3 ft.}{6 ft.} \) = \( \frac{60 ft⋅lb}{6 ft.} \) = 10 lbs.

4 If this lever is in equilibrium with an effort force of 8.33 ft. lb. at the blue arrow and a resistance force of 5 ft. lb. at the green box, what is its mechanical advantage?
48% Answer Correctly
0.9
0.6
2.1
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 = \( \frac{F_r}{F_e} \) = \( \frac{5 ft.}{8.33 ft.} \) = 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

The measure of how much of the power put into a machine is turned into movement or force is called:

56% Answer Correctly

mechanical advantage

efficiency

force multiplication

power
Solution

The efficiency of a machine describes how much of the power put into the machine is turned into movement or force. A 100% efficient machine would turn all of the input power into output movement or force. However, no machine is 100% efficient due to friction, heat, wear and other imperfections that consume input power without delivering any output.