ASVAB Mechanical Comprehension Practice Test 852873 Results

Your Results Global Average
Questions 5 5
Correct 0 2.93
Score 0% 59%

Review

1 If the handles of a wheelbarrow are 2.0 ft. from the wheel axle, how many pounds of force must you exert to lift the handles if it's carrying a 190 lbs. load concentrated at a point 1.5 ft. from the axle?
52% Answer Correctly
142.5
219.5
285
253.3
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:
\( F_e = \frac{F_r d_r}{d_e} \)
\( F_e = \frac{190 \times 1.5}{2.0} \)
\( F_e = \frac{285.0}{2.0} \)
\( F_e = 142.5 \)
2 If the green box weighs 65 lbs. and is 5 ft. from the fulcrum, how far from the fulcrum would a 35 lbs. weight need to be placed to balance the lever?
61% Answer Correctly
9.29 ft.
2.32 ft.
37.14 ft.
18.57 ft.
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 db, our missing value, and plugging in our variables yields:

db = \( \frac{R_ad_a}{R_b} \) = \( \frac{65 lbs. \times 5 ft.}{35 lbs.} \) = \( \frac{325 ft⋅lb}{35 lbs.} \) = 9.29 ft.

3 If A = 5 ft. and the green box weighs 40 lbs. what is the torque acting on the A side of this lever?
75% Answer Correctly
600 ft⋅lb
200 ft⋅lb
66 ft⋅lb
100 ft⋅lb
Solution
For a lever, torque is weight x distance from the fulcrum which, in this case, is: 40 ft. x 5 lbs. = 200 ft⋅lb
4

Which class of lever offers no mechanical advantage?

45% Answer Correctly

third

first

second

none of these, all levers offer mechanical advantage
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.

5

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

59% Answer Correctly

increase the force acting at the blue arrow

shorten the ramp

lower the force acting at the blue arrow

lengthen the ramp
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.