ASVAB Mechanical Comprehension Practice Test 568949 Results

Your Results Global Average
Questions 5 5
Correct 0 3.13
Score 0% 63%

Review

1 A = 4 ft., the green box weighs 5 lbs., and the blue box weighs 30 lbs. What does distance B need to be for this lever to balance?
65% Answer Correctly
2.67 ft.
1.33 ft.
0.67 ft.
0.22 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:

5 lbs. x 4 ft. = 30 lbs. x dB

dB = \( \frac{5 \times 4 ft⋅lb}{30 lbs.} \) = \( \frac{20 ft⋅lb}{30 lbs.} \) = 0.67 ft.

2

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

78% Answer Correctly

concrete

steel

ice

marble
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

Two gears are connected and the larger gear drives the smaller gear. The speed of rotation will __________ and the torque will __________.

60% Answer Correctly

increase, decrease

increase, increase

decrease, increase

decrease, decrease
Solution

Connected gears of different numbers of teeth are used together to change the rotational speed and torque of the input force. If the smaller gear drives the larger gear, the speed of rotation will be reduced and the torque will increase. If the larger gear drives the smaller gear, the speed of rotation will increase and the torque will be reduced.

4 If a 70 lbs. weight is placed 1 ft. from the fulcrum at the blue arrow and the green box is 8 ft. from the fulcrum, how much would the green box have to weigh to balance the lever?
61% Answer Correctly
2.92 lbs.
70 lbs.
17.5 lbs.
8.75 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 Ra, our missing value, and plugging in our variables yields:

Ra = \( \frac{R_bd_b}{d_a} \) = \( \frac{70 lbs. \times 1 ft.}{8 ft.} \) = \( \frac{70 ft⋅lb}{8 ft.} \) = 8.75 lbs.

5

Which of the following represents the force a surface exerts when an object presses against it?

49% Answer Correctly

normal force

counter force

friction

mass
Solution

Normal force (FN) represents the force a surface exerts when an object presses against it.