ASVAB Mechanical Comprehension Practice Test 232872 Results

Your Results Global Average
Questions 5 5
Correct 0 3.29
Score 0% 66%

Review

1 If the green box weighs 75 lbs. and is 5 ft. from the fulcrum, how far from the fulcrum would a 30 lbs. weight need to be placed to balance the lever?
61% Answer Correctly
50 ft.
0 ft.
4.17 ft.
12.5 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 = \( \frac{R_ad_a}{R_b} \) = \( \frac{75 lbs. \times 5 ft.}{30 lbs.} \) = \( \frac{375 ft⋅lb}{30 lbs.} \) = 12.5 ft.

2

A wedge converts force applied to its blunt end into force __________ its inclined surface.

57% Answer Correctly

along

parallel to

perpendicular to

opposite to
Solution

The wedge is a moving inclined plane that is used to lift, hold, or break apart an object. A wedge converts force applied to its blunt end into force perpendicular to its inclined surface. In contrast to a stationary plane where force is applied to the object being moved, with a wedge the object is stationary and the force is being applied to the plane. Examples of a wedge include knives and chisels.

3

Which of the following is the formula for torque?

61% Answer Correctly

τ = F/r2

τ = rF

τ = F/r

τ = r/F
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 you lift a 43 lbs. rock 50 ft. from the ground, how much work have you done?
70% Answer Correctly
None of these is correct
0 ft⋅lb
2150 ft⋅lb
93 ft⋅lb
Solution
Work is force times distance. In this case, the force is the weight of the rock so:
\( W = F \times d \)
\( W = 43 \times 50 \)
\( W = 2150 \)
5 How much resistance could a 130 lb. effort force lift using a block and tackle pulley that has 4 ropes supporting the resistance?
81% Answer Correctly
523 lbs.
521.5 lbs.
260 lbs.
520 lbs.
Solution

The mechanical advantage (MA) of a block and tackle pulley is equal to the number of times the effort force changes direction. An easy way to count how many times the effort force changes direction is to count the number of ropes that support the resistance which, in this problem, is 4. With a MA of 4, a 130 lbs. effort force could lift 130 lbs. x 4 = 520 lbs. resistance.