ASVAB Mechanical Comprehension Practice Test 884438 Results

Your Results Global Average
Questions 5 5
Correct 0 3.21
Score 0% 64%

Review

1 If you have a gear train with two gears, the first with 20 teeth and the second with 4 teeth, how many revolutions does the second gear make for each revolution of the first gear?
78% Answer Correctly
8
5
15
5.5
Solution

The gear ratio (Vr) of a gear train is the product of the gear ratios between the pairs of meshed gears. Let N represent the number of teeth for each gear:

Vr = \( \frac{N_1}{N_2} \) \( \frac{N_2}{N_3} \) \( \frac{N_3}{N_4} \) ... \( \frac{N_n}{N_{n+1}} \)

In this problem, we have only two gears so the equation becomes:

Vr = \( \frac{N_1}{N_2} \) = \( \frac{20}{4} \) = 5

2 If the green box weighs 50 lbs. and is 5 ft. from the fulcrum, how far from the fulcrum would a 25 lbs. force need to be applied to balance the lever?
58% Answer Correctly
0 ft.
5 ft.
10 ft.
20 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 = \( \frac{R_ad_a}{R_b} \) = \( \frac{50 lbs. \times 5 ft.}{25 lbs.} \) = \( \frac{250 ft⋅lb}{25 lbs.} \) = 10 ft.

3

What is the first step to solving a problem where multiple forces are acting on an object?

61% Answer Correctly

calculate the net force

calculate the total force

calculate kinetic energy

calculate potential energy
Solution

In mechanics, multiple forces are often acting on a particular object and, taken together, produce the net force acting on that object. Like force, net force is a vector quantity in that it has magnitude and direction.

4 30 lbs. of effort is used by a machine to lift a 180 lbs. box. What is the mechanical advantage of the machine?
84% Answer Correctly
6.6
6
18
3
Solution

Mechanical advantage is resistance force divided by effort force:

MA = \( \frac{F_r}{F_e} \) = \( \frac{180 lbs.}{30 lbs.} \) = 6

5 What is the power output of a 4 hp engine that's 35% efficient?
40% Answer Correctly
0 \( \frac{ft⋅lb}{s} \)
770 \( \frac{ft⋅lb}{s} \)
192.5 \( \frac{ft⋅lb}{s} \)
2310 \( \frac{ft⋅lb}{s} \)
Solution
\( Efficiency = \frac{Power_{out}}{Power_{in}} \times 100 \)
Solving for power out: \( P_{o} = \frac{E \times P_{i}}{100} \)
Knowing that 1 hp = 550 \( \frac{ft⋅lb}{s} \), Pi becomes 4 hp x 550 \( \frac{ft⋅lb}{s} \) = 2200 \( \frac{ft⋅lb}{s} \)
\( P_{o} = \frac{E \times P_{i}}{100} = \frac{35 \times 2200 \frac{ft⋅lb}{s}}{100} \) \( = \frac{77000 \frac{ft⋅lb}{s}}{100} \) = 770 \( \frac{ft⋅lb}{s} \)