ASVAB Mechanical Comprehension Practice Test 973760 Results

Your Results Global Average
Questions 5 5
Correct 0 2.79
Score 0% 56%

Review

1 If 5 lbs. of force is applied 6 ft. from the fulcrum at the blue arrow and the green box is 4 ft. from the fulcrum, how much would the green box have to weigh to balance the lever?
62% Answer Correctly
7.5 lbs.
2.5 lbs.
22.5 lbs.
1.88 lbs.
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 Ra, our missing value, and plugging in our variables yields:

Ra = \( \frac{R_bd_b}{d_a} \) = \( \frac{5 lbs. \times 6 ft.}{4 ft.} \) = \( \frac{30 ft⋅lb}{4 ft.} \) = 7.5 lbs.

2

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

57% Answer Correctly

idler gear

driven gear

driver gear

input 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 If the radius of the axle is 5 and the radius of the wheel is 10, what is the mechanical advantage of this wheel and axle configuration?
36% Answer Correctly
0
5
1
-5
Solution

The mechanical advantage of a wheel and axle lies in the difference in radius between the inner (axle) wheel and the outer wheel. But, this mechanical advantage is only realized when the input effort and load are applied to different wheels. Applying both input effort and load to the same wheel results in a mechanical advantage of 1.

4 If you have a gear train with two gears, the first with 36 teeth and the second with 4 teeth, how many revolutions does the second gear make for each revolution of the first gear?
77% Answer Correctly
13.5
8.1
27
9
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 = \( \frac{N_1}{N_2} \) = \( \frac{36}{4} \) = 9

5 If A = 9 ft., B = 2 ft., C = 4 ft., the green box weighs 25 lbs. and the blue box weighs 35 lbs., what does the orange box have to weigh for this lever to balance?
43% Answer Correctly
12.92 lbs.
38.75 lbs.
116.25 lbs.
225 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:

25 lbs. x 9 ft. = 35 lbs. x 2 ft. + fC x 4 ft.

225 ft. lbs. = 70 ft. lbs. + fC x 4 ft.

fC = \( \frac{225 ft. lbs. - 70 ft. lbs.}{4 ft.} \) = \( \frac{155 ft. lbs.}{4 ft.} \) = 38.75 lbs.