ASVAB Mechanical Comprehension Practice Test 474340 Results

Your Results Global Average
Questions 5 5
Correct 0 2.95
Score 0% 59%

Review

1 If the green box weighs 40 lbs. and 15 lbs. of force is applied 7 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?
55% Answer Correctly
1.31 ft.
2.63 ft.
10.5 ft.
5.25 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 da, our missing value, and plugging in our variables yields:

da = \( \frac{R_bd_b}{R_a} \) = \( \frac{15 lbs. \times 7 ft.}{40 lbs.} \) = \( \frac{105 ft⋅lb}{40 lbs.} \) = 2.63 ft.

2 If the handles of a wheelbarrow are 1.0 ft. from the wheel axle, how many pounds of force must you exert to lift the handles if it's carrying a 230 lbs. load concentrated at a point 1.5 ft. from the axle?
52% Answer Correctly
345
206.5
None of these is correct
-89
Solution
This problem describes a second-class lever and, for a second class lever, the effort force multiplied by the effort distance equals the resistance force multipied by the resistance distance: Fede = Frdr. In this problem we're looking for effort force:
\( F_e = \frac{F_r d_r}{d_e} \)
\( F_e = \frac{230 \times 1.5}{1.0} \)
\( F_e = \frac{345.0}{1.0} \)
\( F_e = 345 \)
3 80 lbs. of effort is used by a machine to lift a 560 lbs. box. What is the mechanical advantage of the machine?
84% Answer Correctly
3
10
7
9
Solution

Mechanical advantage is resistance force divided by effort force:

MA = \( \frac{F_r}{F_e} \) = \( \frac{560 lbs.}{80 lbs.} \) = 7

4

Which class of lever is used to increase force on an object in the same direction as the force is applied?

52% Answer Correctly

all of these

third

first

second
Solution

A second-class lever is used to increase force on an object in the same direction as the force is applied. This lever requires a smaller force to lift a larger load but the force must be applied over a greater distance. The fulcrum is placed at one end of the lever and mechanical advantage increases as the object being lifted is moved closer to the fulcrum or the length of the lever is increased. An example of a second-class lever is a wheelbarrow.

5 If the radius of the axle is 5 and the radius of the wheel is 8, what is the mechanical advantage of this wheel and axle configuration?
52% Answer Correctly
-3
1.6
5
0.63
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 8 and the output radius (where the resistance is being applied) is 5 for a mechanical advantage of \( \frac{8}{5} \) = 1.6