ASVAB Mechanical Comprehension Practice Test 266168 Results

Your Results Global Average
Questions 5 5
Correct 0 2.89
Score 0% 58%

Review

1 A = 9 ft., the green box weighs 35 lbs., and the blue box weighs 75 lbs. What does distance B need to be for this lever to balance?
65% Answer Correctly
315 ft.
4.2 ft.
0 ft.
8.4 ft.
Solution
In order for this lever to balance, the torque acting on side A must equal the torque acting on side B. Torque is weight x distance from the fulcrum which means that the following must be true for the lever to balance:

fAdA = fBdB

For this problem, the equation becomes:

35 lbs. x 9 ft. = 75 lbs. x dB

dB = \( \frac{35 \times 9 ft⋅lb}{75 lbs.} \) = \( \frac{315 ft⋅lb}{75 lbs.} \) = 4.2 ft.

2 The radius of the axle is 5, the radius of the wheel is 8, and the blue box weighs 25 lbs. What is the effort force necessary to balance the load?
53% Answer Correctly
40 lbs.
13 lbs.
15.63 lbs.
12.8 lbs.
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

MA = \( \frac{load}{effort} \) so effort = \( \frac{load}{MA} \) = \( \frac{25 lbs.}{1.6} \) = 15.63 lbs.

3

Which of the following is the formula for torque?

62% Answer Correctly

τ = rF

τ = F/r

τ = r/F

τ = F/r2
Solution

Torque measures force applied during rotation: τ = rF.  Torque (τ, the Greek letter tau) = the radius of the lever arm (r) multiplied by the force (F) applied. Radius is measured from the center of rotation or fulcrum to the point at which the perpendicular force is being applied. The resulting unit for torque is newton-meter (N-m) or foot-pound (ft-lb).

4 If the green box weighs 25 lbs. and is 7 ft. from the fulcrum, how much weight would need to be placed at the blue arrow to balance the lever if the arrow's distance from the fulcrum is 4 ft.?
63% Answer Correctly
131.25 lbs.
43.75 lbs.
100 lbs.
6 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 Rb, our missing value, and plugging in our variables yields:

Rb = \( \frac{R_ad_a}{d_b} \) = \( \frac{25 lbs. \times 7 ft.}{4 ft.} \) = \( \frac{175 ft⋅lb}{4 ft.} \) = 43.75 lbs.

5

Which class of lever offers no mechanical advantage?

45% Answer Correctly

second

first

third

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.