ASVAB Mechanical Comprehension Practice Test 257068 Results

Your Results Global Average
Questions 5 5
Correct 0 2.75
Score 0% 55%

Review

1 80 lbs. of effort is used by a machine to lift a 400 lbs. box. What is the mechanical advantage of the machine?
84% Answer Correctly
5
2
4.5
6
Solution

Mechanical advantage is resistance force divided by effort force:

MA = \( \frac{F_r}{F_e} \) = \( \frac{400 lbs.}{80 lbs.} \) = 5

2

What's the last gear in a gear train called?

38% Answer Correctly

output gear

idler gear

driven gear

driver gear
Solution

A gear train is two or more gears linked together. Gear trains are designed to increase or reduce the speed or torque outpout of a rotating system or change the direction of its output. The first gear in the chain is called the driver and the last gear in the chain the driven gear with the gears between them called idler gears.

3 How much work can a 8 hp engine do in 5 seconds?
53% Answer Correctly
16 ft⋅lb
0 ft⋅lb
22000 ft⋅lb
2 ft⋅lb
Solution
Horsepower (hp) is a common measure of power output for complex machines. By definition, a 1 hp machine does 550 ft⋅lb of work in 1 second: 1 hp = 550 ft⋅lb/s. Substituting the variables for this problem gives us:
\( W = 8 hp \times 550 \frac{ft⋅lb}{s} \times 5s = 22000 ft⋅lb \)
4 If A = 8 ft., B = 3 ft., C = 4 ft., the green box weighs 45 lbs. and the blue box weighs 65 lbs., what does the orange box have to weigh for this lever to balance?
44% Answer Correctly
82.5 lbs.
360 lbs.
20.63 lbs.
41.25 lbs.
Solution
In order for this lever to balance, the torque acting on each side of the fulrum must be equal. So, the torque produced by A must equal the torque produced by B and C. Torque is weight x distance from the fulcrum which means that the following must be true for the lever to balance:

fAdA = fBdB + fCdC

For this problem, this equation becomes:

45 lbs. x 8 ft. = 65 lbs. x 3 ft. + fC x 4 ft.

360 ft. lbs. = 195 ft. lbs. + fC x 4 ft.

fC = \( \frac{360 ft. lbs. - 195 ft. lbs.}{4 ft.} \) = \( \frac{165 ft. lbs.}{4 ft.} \) = 41.25 lbs.

5 If a 60 lbs. weight is placed 7 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
52.5 lbs.
157.5 lbs.
105 lbs.
420 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 = \( \frac{R_bd_b}{d_a} \) = \( \frac{60 lbs. \times 7 ft.}{8 ft.} \) = \( \frac{420 ft⋅lb}{8 ft.} \) = 52.5 lbs.