ASVAB Mechanical Comprehension Practice Test 12495 Results

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

Review

1 If the green box weighs 25 lbs. and is 5 ft. from the fulcrum, how far from the fulcrum would a 65 lbs. force need to be applied to balance the lever?
58% Answer Correctly
1.92 ft.
3.85 ft.
5.77 ft.
0.64 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 db, our missing value, and plugging in our variables yields:

db = \( \frac{R_ad_a}{R_b} \) = \( \frac{25 lbs. \times 5 ft.}{65 lbs.} \) = \( \frac{125 ft⋅lb}{65 lbs.} \) = 1.92 ft.


2

A ramp is an example of which kind of simple machine?

84% Answer Correctly

first-class lever

wedge

none of these

inclined plane


Solution

An inclined plane is a simple machine that reduces the force needed to raise an object to a certain height. Work equals force x distance and, by increasing the distance that the object travels, an inclined plane reduces the force necessary to raise it to a particular height. In this case, the mechanical advantage is to make the task easier. An example of an inclined plane is a ramp.


3

What type of load creates different stresses at different locations on a structure?

60% Answer Correctly

non-uniformly distributed load

impact load

static uniformly distributed load

dynamic load


Solution

A concentrated load acts on a relatively small area of a structure, a static uniformly distributed load doesn't create specific stress points or vary with time, a dynamic load varies with time or affects a structure that experiences a high degree of movement, an impact load is sudden and for a relatively short duration and a non-uniformly distributed load creates different stresses at different locations on a structure.


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


5 If you have a gear train with three gears, the first with 22 teeth, the second with 10 teeth, and the third with 8 teeth, what is its mechanical advantage?
51% Answer Correctly
1.8
2.8
4.3
3

Solution

The mechanical advantage of a gear train is its gear ratio. The gear ratio (Vr) is the product of the gear ratios between the pairs of meshed gears. Let N represent the number of teeth for each gear:

Vr = \( \frac{N_1}{N_2} \) \( \frac{N_2}{N_3} \) \( \frac{N_3}{N_4} \) ... \( \frac{N_n}{N_{n+1}} \)

In this problem, we have three gears so the equation becomes:

Vr = \( \frac{N_1}{N_2} \) \( \frac{N_2}{N_3} \) = \( \frac{22}{10} \) \( \frac{10}{8} \) = \( \frac{22}{8} \) = 2.8