ASVAB Mechanical Comprehension Practice Test 915035 Results

Your Results Global Average
Questions 5 5
Correct 0 2.46
Score 0% 49%

Review

1

The mechanical advantage of a third class lever is always:

37% Answer Correctly

less than one

equal to one

greater than one

not equal to one
Solution

A third class lever is designed to multiply distance and speed at the expense of effort force. Because the effort force is greater than the resistance, the mechanical advantage of a third class lever is always less than one.

An example of a third class lever is a broom. The fulcrum is at your hand on the end of the broom, the effort force is your other hand in the middle, and the resistance is at the bottom bristles. The effort force of your hand in the middle multiplies the distance and speed of the bristles at the bottom but at the expense of producing a brushing force that's less than the force you're applying with your hand.

2 If the green box weighs 35 lbs. and 15 lbs. of force is applied 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?
55% Answer Correctly
0 ft.
2.14 ft.
6.43 ft.
7 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 = \( \frac{R_bd_b}{R_a} \) = \( \frac{15 lbs. \times 5 ft.}{35 lbs.} \) = \( \frac{75 ft⋅lb}{35 lbs.} \) = 2.14 ft.

3

Two or more pulleys used together are called:

71% Answer Correctly

block and tackle

third-class lever

gears

wheel and axle
Solution

Two or more pulleys used together constitute a block and tackle which, unlike a fixed pulley, does impart mechanical advantage as a function of the number of pulleys that make up the arrangement.  So, for example, a block and tackle with three pulleys would have a mechanical advantage of three.

4 If the handles of a wheelbarrow are 1.5 ft. from the wheel axle and the load is concentrated at a point 0.5 ft. from the axle, how many pounds of load will a 140 lbs. force lift?
47% Answer Correctly
None of these is correct
37.3
46.7
420
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 resistance force:
\( F_r = \frac{F_e d_e}{d_r} \)
\( F_r = \frac{140 \times 1.5}{0.5} \)
\( F_r = \frac{210.0}{0.5} \)
\( F_r = 420 \)
5 If the radius of the axle is 7 and the radius of the wheel is 12, what is the mechanical advantage of this wheel and axle configuration?
36% Answer Correctly
5
12
1
1
Solution

The mechanical advantage of a wheel and axle lies in the difference in radius between the inner (axle) wheel and the outer wheel. But, this mechanical advantage is only realized when the input effort and load are applied to different wheels. Applying both input effort and load to the same wheel results in a mechanical advantage of 1.