ASVAB Mechanical Comprehension Practice Test 21759 Results

Your Results Global Average
Questions 5 5
Correct 0 3.51
Score 0% 70%

Review

1 If the green box weighs 20 lbs. and 65 lbs. of force is applied 1 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
3.25 ft.
1.08 ft.
6.5 ft.
0.81 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 = \( \frac{R_bd_b}{R_a} \) = \( \frac{65 lbs. \times 1 ft.}{20 lbs.} \) = \( \frac{65 ft⋅lb}{20 lbs.} \) = 3.25 ft.

2 What's the mechanical advantage of a wedge that's 2 inches wide and 14 inches long?
83% Answer Correctly
8.5
7
6.3
14
Solution

The mechanical advantage (MA) of a wedge is its length divided by its thickness:

MA = \( \frac{l}{t} \) = \( \frac{14 in.}{2 in.} \) = 7

3 What is the efficiency of a machine has work input of 170 ft⋅lb and work output of 42 ft⋅lb?
68% Answer Correctly
25%
12%
0%
4%
Solution
Due to friction, a machine will never be able to utilize 100% of its work input. A certain percentage of that input will be lost in overcoming friction within the machine. Effeciency is a measure of how much of a machine's work input can be turned into useful work output and is calculated by dividing work output by work input and multiplying the result by 100:
\( Efficiency = \frac{Work_{out}}{Work_{in}} \times 100 \) \( = \frac{42 ft⋅lb}{170 ft⋅lb} \times 100 \) \( = 25% \) %
4

Which of the following will increase the mechanical advantage of this inclined plane?

59% Answer Correctly

lengthen the ramp

lower the force acting at the blue arrow

shorten the ramp

increase the force acting at the blue arrow
Solution

The mechanical advantage (MA) of an inclined plane is the effort distance divided by the resistance distance. In order to increase mechanical advantage, this ratio must increase which means making the effort distance longer and this can be accomplished by lengthening the length of the ramp.

5

An object's resistance to changes in direction is known as:

82% Answer Correctly

inertia

weight

kinetic energy

mass
Solution

The more mass a substance has the more force is required to move it or to change its direction. This resistance to changes in direction is known as inertia.