ASVAB Mechanical Comprehension Practice Test 464608 Results

Your Results Global Average
Questions 5 5
Correct 0 3.27
Score 0% 65%

Review

1 If the green box weighs 40 lbs. and is 9 ft. from the fulcrum, how far from the fulcrum would a 55 lbs. force need to be applied to balance the lever?
58% Answer Correctly
6.55 ft.
4 ft.
0 ft.
19.64 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 db, our missing value, and plugging in our variables yields:

db = \( \frac{R_ad_a}{R_b} \) = \( \frac{40 lbs. \times 9 ft.}{55 lbs.} \) = \( \frac{360 ft⋅lb}{55 lbs.} \) = 6.55 ft.

2

Which of the following is the formula for torque?

61% Answer Correctly

τ = r/F

τ = F/r2

τ = F/r

τ = rF
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).

3

Tension is a force that does which of the following?

76% Answer Correctly

heats up an object

slows an object

compacts an object

stretches an object
Solution

Tension is a force that stretches or elongates something. When a cable or rope is used to pull an object, for example, it stretches internally as it accepts the weight that it's moving. Although tension is often treated as applying equally to all parts of a material, it's greater at the places where the material is under the most stress.

4 If input effort is 200 ft⋅lb, what output effort will be produced by a machine with a mechanical advantage of 9?
79% Answer Correctly
1800 ft⋅lb
0ft⋅lb
3600ft⋅lb
7200ft⋅lb
Solution
Mechanical advantage is the ratio of output force to input force and tells us by how many times a machine multiplies input effort. So, a machine with a mechanical advantage of 9 will multiply an input effort of 200 ft⋅lb by 9 to produce an output effort of 1800 ft⋅lb.
5 The radius of the axle is 3, the radius of the wheel is 6, and the blue box weighs 70 lbs. What is the effort force necessary to balance the load?
53% Answer Correctly
5 lbs.
12 lbs.
35 lbs.
6 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 6 and the output radius (where the resistance is being applied) is 3 for a mechanical advantage of \( \frac{6}{3} \) = 2.0

MA = \( \frac{load}{effort} \) so effort = \( \frac{load}{MA} \) = \( \frac{70 lbs.}{2.0} \) = 35 lbs.