ASVAB Mechanical Comprehension Practice Test 156503 Results

Your Results Global Average
Questions 5 5
Correct 0 2.88
Score 0% 58%

Review

1

Which of the following is not true of a  first-class lever?

51% Answer Correctly

decreases distance

changes the direction of force

increases force

increases distance
Solution

A first-class lever is used to increase force or distance while changing the direction of the force. The lever pivots on a fulcrum and, when a force is applied to the lever at one side of the fulcrum, the other end moves in the opposite direction. The position of the fulcrum also defines the mechanical advantage of the lever. If the fulcrum is closer to the force being applied, the load can be moved a greater distance at the expense of requiring a greater input force. If the fulcrum is closer to the load, less force is required but the force must be applied over a longer distance. An example of a first-class lever is a seesaw / teeter-totter.

2

Connected gears of different numbers of teeth are used together to change which of the following charasteristics of the input force?

66% Answer Correctly

energy

rotational direction

force

torque
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.

3 If the green box weighs 15 lbs. and is 1 ft. from the fulcrum, how far from the fulcrum would a 50 lbs. weight need to be placed to balance the lever?
61% Answer Correctly
15 ft.
0.6 ft.
0.3 ft.
0 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 = \( \frac{R_ad_a}{R_b} \) = \( \frac{15 lbs. \times 1 ft.}{50 lbs.} \) = \( \frac{15 ft⋅lb}{50 lbs.} \) = 0.3 ft.

4

The measure of how much of the power put into a machine is turned into movement or force is called:

56% Answer Correctly

mechanical advantage

force multiplication

power

efficiency
Solution

The efficiency of a machine describes how much of the power put into the machine is turned into movement or force. A 100% efficient machine would turn all of the input power into output movement or force. However, no machine is 100% efficient due to friction, heat, wear and other imperfections that consume input power without delivering any output.

5 A 490 lb. barrel is rolled up a 10 ft. ramp to a platform that's 3 ft. tall. What effort is required to move the barrel?
53% Answer Correctly
150 lbs.
294 lbs.
147 lbs.
149 lbs.
Solution

This problem describes an inclined plane and, for an inclined plane, the effort force multiplied by the effort distance equals the resistance force multipied by the resistance distance:

Fede = Frdr

Plugging in the variables from this problem yields:

Fe x 10 ft. = 490 lbs. x 3 ft.
Fe = \( \frac{1470 ft⋅lb}{10 ft.} \) = 147 lbs.