ASVAB Mechanical Comprehension Practice Test 175905 Results

Your Results Global Average
Questions 5 5
Correct 0 2.58
Score 0% 52%

Review

1 If a 75 lbs. weight is placed 7 ft. from the fulcrum at the blue arrow and the green box is 4 ft. from the fulcrum, how much would the green box have to weigh to balance the lever?
61% Answer Correctly
0 lbs.
262.5 lbs.
131.25 lbs.
43.75 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 = \( \frac{R_bd_b}{d_a} \) = \( \frac{75 lbs. \times 7 ft.}{4 ft.} \) = \( \frac{525 ft⋅lb}{4 ft.} \) = 131.25 lbs.

2

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

56% Answer Correctly

efficiency

force multiplication

power

mechanical advantage
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.

3 A 300 lb. barrel is rolled up a 5 ft. ramp to a platform that's 1 ft. tall. What effort is required to move the barrel?
53% Answer Correctly
30 lbs.
60 lbs.
66 lbs.
61.5 lbs.
Solution

This problem describes an inclined plane and, for an inclined plane, the effort force multiplied by the effort distance equals the resistance force multipied by the resistance distance:

Fede = Frdr

Plugging in the variables from this problem yields:

Fe x 5 ft. = 300 lbs. x 1 ft.
Fe = \( \frac{300 ft⋅lb}{5 ft.} \) = 60 lbs.

4

The principle of conservation of mechanical energy states that, as long as no other forces are applied, what will remain constant as an object falls?

45% Answer Correctly

total mechanical energy

kinetic energy

acceleration

potential energy
Solution

As an object falls, its potential energy is converted into kinetic energy. The principle of conservation of mechanical energy states that, as long as no other forces are applied, total mechanical energy (PE + KE) of the object will remain constant at all points in its descent.

5 If A = 9 ft., B = 2 ft., C = 8 ft., the green box weighs 25 lbs. and the blue box weighs 30 lbs., what does the orange box have to weigh for this lever to balance?
44% Answer Correctly
20.63 lbs.
2 lbs.
225 lbs.
82.5 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:

25 lbs. x 9 ft. = 30 lbs. x 2 ft. + fC x 8 ft.

225 ft. lbs. = 60 ft. lbs. + fC x 8 ft.

fC = \( \frac{225 ft. lbs. - 60 ft. lbs.}{8 ft.} \) = \( \frac{165 ft. lbs.}{8 ft.} \) = 20.63 lbs.