ASVAB Mechanical Comprehension Practice Test 648887 Results

Your Results Global Average
Questions 5 5
Correct 0 2.81
Score 0% 56%

Review

1 A = 8 ft., the green box weighs 40 lbs., and the blue box weighs 90 lbs. What does distance B need to be for this lever to balance?
65% Answer Correctly
0.89 ft.
3.56 ft.
11 ft.
320 ft.
Solution
In order for this lever to balance, the torque acting on side A must equal the torque acting on side B. Torque is weight x distance from the fulcrum which means that the following must be true for the lever to balance:

fAdA = fBdB

For this problem, the equation becomes:

40 lbs. x 8 ft. = 90 lbs. x dB

dB = \( \frac{40 \times 8 ft⋅lb}{90 lbs.} \) = \( \frac{320 ft⋅lb}{90 lbs.} \) = 3.56 ft.

2 If a 10 lbs. weight is placed 5 ft. from the fulcrum at the blue arrow and the green box is 8 ft. from the fulcrum, how much would the green box have to weigh to balance the lever?
61% Answer Correctly
6.25 lbs.
1.56 lbs.
2 lbs.
0 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 Ra, our missing value, and plugging in our variables yields:

Ra = \( \frac{R_bd_b}{d_a} \) = \( \frac{10 lbs. \times 5 ft.}{8 ft.} \) = \( \frac{50 ft⋅lb}{8 ft.} \) = 6.25 lbs.

3

The advantage of using a third-class lever is that it increases:

37% Answer Correctly

the distance traveled by the load

the speed of the load

the force applied to the load

the mechanical advantage of the lever
Solution

A third-class lever is used to increase distance traveled by an object in the same direction as the force applied. The fulcrum is at one end of the lever, the object at the other, and the force is applied between them. This lever does not impart a mechanical advantage as the effort force must be greater than the load but does impart extra speed to the load. Examples of third-class levers are shovels and tweezers.

4

What defines the mechanical advantage of a first class lever?

65% Answer Correctly

position of the fulcrum

output force 

input force

output distance
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.

5 The radius of the axle is 5, the radius of the wheel is 6, and the blue box weighs 60 lbs. What is the effort force necessary to balance the load?
53% Answer Correctly
6 lbs.
7.2 lbs.
6.2 lbs.
50 lbs.
Solution

The mechanical advantage of a wheel and axle is the input radius divided by the output radius:

MA = \( \frac{r_i}{r_o} \)

In this case, the input radius (where the effort force is being applied) is 6 and the output radius (where the resistance is being applied) is 5 for a mechanical advantage of \( \frac{6}{5} \) = 1.2

MA = \( \frac{load}{effort} \) so effort = \( \frac{load}{MA} \) = \( \frac{60 lbs.}{1.2} \) = 50 lbs.