ASVAB Mechanical Comprehension Practice Test 945711 Results

Your Results Global Average
Questions 5 5
Correct 0 2.73
Score 0% 55%

Review

1

Depending on where you apply effort and resistance, the wheel and axle can multiply:

45% Answer Correctly

force or distance

speed or power

force or speed

power or distance
Solution

If you apply the resistance to the axle and the effort to the wheel, the wheel and axle will multiply force and if you apply the resistance to the wheel and the effort to the axle, it will multiply speed.

2

Which of the following is the formula for gravitational potential energy?

61% Answer Correctly

\(PE = { 1 \over 2} mv^2\)

\(PE = mg^2h\)

\(PE = mgh\)

\(PE = { 1 \over 2} mg^2\)
Solution

Gravitational potential energy is energy by virtue of gravity. The higher an object is raised above a surface the greater the distance it must fall to reach that surface and the more velocity it will build as it falls. For gravitational potential energy, PE = mgh where m is mass (kilograms), h is height (meters), and g is acceleration due to gravity which is a constant (9.8 m/s2).

3 If A = 10 ft., B = 3 ft., C = 8 ft., the green box weighs 50 lbs. and the blue box weighs 65 lbs., what does the orange box have to weigh for this lever to balance?
44% Answer Correctly
16 lbs.
19.06 lbs.
38.13 lbs.
12.71 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:

50 lbs. x 10 ft. = 65 lbs. x 3 ft. + fC x 8 ft.

500 ft. lbs. = 195 ft. lbs. + fC x 8 ft.

fC = \( \frac{500 ft. lbs. - 195 ft. lbs.}{8 ft.} \) = \( \frac{305 ft. lbs.}{8 ft.} \) = 38.13 lbs.

4 If the green box weighs 10 lbs. and is 3 ft. from the fulcrum, how far from the fulcrum would a 40 lbs. weight need to be placed to balance the lever?
61% Answer Correctly
0 ft.
1.5 ft.
0.75 ft.
0.38 ft.
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 db, our missing value, and plugging in our variables yields:

db = \( \frac{R_ad_a}{R_b} \) = \( \frac{10 lbs. \times 3 ft.}{40 lbs.} \) = \( \frac{30 ft⋅lb}{40 lbs.} \) = 0.75 ft.

5

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

61% Answer Correctly

decrease, increase

increase, increase

decrease, decrease

increase, 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.