ASVAB Mechanical Comprehension Practice Test 179272 Results

Your Results Global Average
Questions 5 5
Correct 0 2.93
Score 0% 59%

Review

1

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

61% Answer Correctly

increase, increase

increase, decrease

decrease, decrease

decrease, increase
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.

2 If the green box weighs 75 lbs. and is 1 ft. from the fulcrum, how far from the fulcrum would a 20 lbs. force need to be applied to balance the lever?
58% Answer Correctly
1.88 ft.
3.75 ft.
0.94 ft.
7.5 ft.
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 db, our missing value, and plugging in our variables yields:

db = \( \frac{R_ad_a}{R_b} \) = \( \frac{75 lbs. \times 1 ft.}{20 lbs.} \) = \( \frac{75 ft⋅lb}{20 lbs.} \) = 3.75 ft.

3

A truck is using a rope to pull a car. Tension in the rope is greatest in which of the following places?

50% Answer Correctly

near the car

in the middle

tension is equal in all parts of the rope

near the truck
Solution

Tension is a force that stretches or elongates something. When a cable or rope is used to pull an object, for example, it stretches internally as it accepts the weight that it's moving. Although tension is often treated as applying equally to all parts of a material, it's greater at the places where the material is under the most stress.

4

A a seesaw / teeter-totter is an example of which of the following?

69% Answer Correctly

first-class lever

second-class lever

inclined plane

third-class lever
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.

5

If the handles of a wheelbarrow are 3 ft. from the wheel axle, what force must you exert to lift the handles if it's carrying a 270 lb. load concentrated at a point 0.5 ft. from the axle?

56% Answer Correctly

810 lbs

0.83 lbs

90 lbs

45 lbs
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. Plugging in the variables from this problem yields:

Fe x 3 ft. = 270 lbs x 0.5 ft
Fe = 135 ft-lb. / 3 ft 
Fe = 45 lbs