ASVAB Mechanical Comprehension Practice Test 229683 Results

Your Results Global Average
Questions 5 5
Correct 0 2.77
Score 0% 55%

Review

1 If the handles of a wheelbarrow are 0.5 ft. from the wheel axle, how many pounds of force must you exert to lift the handles if it's carrying a 230 lbs. load concentrated at a point 0.5 ft. from the axle?
52% Answer Correctly
78.1
230
212.3
0
Solution
This problem describes a second-class lever and, for a second class lever, the effort force multiplied by the effort distance equals the resistance force multipied by the resistance distance: Fede = Frdr. In this problem we're looking for effort force:
\( F_e = \frac{F_r d_r}{d_e} \)
\( F_e = \frac{230 \times 0.5}{0.5} \)
\( F_e = \frac{115.0}{0.5} \)
\( F_e = 230 \)
2

A screw is most like which of the following other simple machines?

50% Answer Correctly

inclined plane

first-class lever

block and tackle

wheel and axle
Solution

A screw is an inclined plane wrapped in ridges (threads) around a cylinder. The distance between these ridges defines the pitch of the screw and this distance is how far the screw advances when it is turned once. The mechanical advantage of a screw is its circumference divided by the pitch.

3

Assuming force applied remains constant, which of the following will result in more work being done?

53% Answer Correctly

moving the object with more acceleration

moving the object with more speed

moving the object farther

increasing the coefficient of friction
Solution

Work is accomplished when force is applied to an object: W = Fd where F is force in newtons (N) and d is distance in meters (m). Thus, the more force that must be applied to move an object, the more work is done and the farther an object is moved by exerting force, the more work is done.

4

The mechanical advantage of a wheel and axle is equal to the:

61% Answer Correctly

ratio of the diameters of the wheels

difference in the diameters of the wheels

difference in the lengths of the axles

length of the axle
Solution

A wheel and axle uses two different diameter wheels mounted to a connecting axle. Force is applied to the larger wheel and large movements of this wheel result in small movements in the smaller wheel. Because a larger movement distance is being translated to a smaller distance, force is increased with a mechanical advantage equal to the ratio of the diameters of the wheels. An example of a wheel and axle is the steering wheel of a car.

5 If 65 lbs. of force is applied 7 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
113.75 lbs.
455 lbs.
227.5 lbs.
37.92 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 = \( \frac{R_bd_b}{d_a} \) = \( \frac{65 lbs. \times 7 ft.}{4 ft.} \) = \( \frac{455 ft⋅lb}{4 ft.} \) = 113.75 lbs.