ASVAB Mechanical Comprehension Practice Test 622293 Results

Your Results Global Average
Questions 5 5
Correct 0 3.25
Score 0% 65%

Review

1 How much resistance could a 85 lb. effort force lift using a block and tackle pulley that has 4 ropes supporting the resistance?
81% Answer Correctly
510 lbs.
113 lbs.
340 lbs.
1020 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 85 lbs. effort force could lift 85 lbs. x 4 = 340 lbs. resistance.

2

Which of the following surfaces would have the lowest coefficient of friction?

85% Answer Correctly

tile

concrete

ice

leather
Solution

Coefficient of friction (μ) represents how much two materials resist sliding across each other.  Smooth surfaces like ice have low coefficients of friction while rough surfaces like concrete have high μ.

3 If the green box weighs 35 lbs. and is 1 ft. from the fulcrum, how far from the fulcrum would a 30 lbs. force need to be applied to balance the lever?
58% Answer Correctly
0.58 ft.
2.33 ft.
35 ft.
1.17 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 = \( \frac{R_ad_a}{R_b} \) = \( \frac{35 lbs. \times 1 ft.}{30 lbs.} \) = \( \frac{35 ft⋅lb}{30 lbs.} \) = 1.17 ft.

4 If the handles of a wheelbarrow are 1.0 ft. from the wheel axle, how many pounds of force must you exert to lift the handles if it's carrying a 260 lbs. load concentrated at a point 0.5 ft. from the axle?
52% Answer Correctly
520
130
None of these is correct
84.9
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:
\( F_e = \frac{F_r d_r}{d_e} \)
\( F_e = \frac{260 \times 0.5}{1.0} \)
\( F_e = \frac{130.0}{1.0} \)
\( F_e = 130 \)
5

Which of the following is not a modulus of elasticity?

47% Answer Correctly

stress modulus

stretch modulus

shear modulus

bulk modulus
Solution

The modulus of elasticity measures how much a material or structure will deflect under stress. Stretch modulus is longitudinal stretch (like stretching raw bread dough), shear modulus is longitudinal deflection (like the horizontal displacement of a stack of magzines when a heavy object is placed upon them), and bulk modulus is compression of volume (like the compression of a loaf of bread under a heavy can at the bottom of a grocery bag).