ASVAB Mechanical Comprehension Practice Test 377779 Results

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

Review

1 If A = 8 ft., B = 1 ft., C = 4 ft., the green box weighs 40 lbs. and the blue box weighs 45 lbs., what does the orange box have to weigh for this lever to balance?
43% Answer Correctly
137.5 lbs.
68.75 lbs.
275 lbs.
17.19 lbs.
Solution
In order for this lever to balance, the torque acting on each side of the fulrum must be equal. So, the torque produced by A must equal the torque produced by B and C. Torque is weight x distance from the fulcrum which means that the following must be true for the lever to balance:

fAdA = fBdB + fCdC

For this problem, this equation becomes:

40 lbs. x 8 ft. = 45 lbs. x 1 ft. + fC x 4 ft.

320 ft. lbs. = 45 ft. lbs. + fC x 4 ft.

fC = \( \frac{320 ft. lbs. - 45 ft. lbs.}{4 ft.} \) = \( \frac{275 ft. lbs.}{4 ft.} \) = 68.75 lbs.

2

What is work?

60% Answer Correctly

The movement of an object by a force

Force per unit time

The potential for exertion

Force per unit distance
Solution

Work is accomplished when force is applied to an object: W = Fd where F is force in newtons (N) and d is distance in meters (m). Thus, the more force that must be applied to move an object, the more work is done and the farther an object is moved by exerting force, the more work is done. By definition, work is the displacement of an object resulting from applied force.

3

The mechanical advantage of connected gears is proportional to which characteristic of the gears?

73% Answer Correctly

speed

circumference

diameter

number of teeth
Solution

The mechanical advantage (amount of change in speed or torque) of connected gears is proportional to the number of teeth each gear has. Called gear ratio, it's the ratio of the number of teeth on the larger gear to the number of teeth on the smaller gear.  For example, a gear with 12 teeth connected to a gear with 9 teeth would have a gear ratio of 4:3.

4 The green box weighs 10 lbs. and a 55 lbs. weight is placed 5 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?
57% Answer Correctly
2 ft.
13.75 ft.
27.5 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 da, our missing value, and plugging in our variables yields:

da = \( \frac{R_bd_b}{R_a} \) = \( \frac{55 lbs. \times 5 ft.}{10 lbs.} \) = \( \frac{275 ft⋅lb}{10 lbs.} \) = 27.5 ft.

5 If A = 4 ft. and the green box weighs 45 lbs. what is the torque acting on the A side of this lever?
75% Answer Correctly
180 ft⋅lb
0 ft⋅lb
360 ft⋅lb
720 ft⋅lb
Solution
For a lever, torque is weight x distance from the fulcrum which, in this case, is: 45 ft. x 4 lbs. = 180 ft⋅lb