ASVAB Mechanical Comprehension Practice Test 395698 Results

Your Results Global Average
Questions 5 5
Correct 0 3.15
Score 0% 63%

Review

1 If the green box weighs 20 lbs. and is 9 ft. from the fulcrum, how much weight would need to be placed at the blue arrow to balance the lever if the arrow's distance from the fulcrum is 8 ft.?
63% Answer Correctly
67.5 lbs.
22.5 lbs.
7.5 lbs.
2 lbs.
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 Rb, our missing value, and plugging in our variables yields:

Rb = \( \frac{R_ad_a}{d_b} \) = \( \frac{20 lbs. \times 9 ft.}{8 ft.} \) = \( \frac{180 ft⋅lb}{8 ft.} \) = 22.5 lbs.

2

Which class of lever offers no mechanical advantage?

45% Answer Correctly

third

none of these, all levers offer mechanical advantage

second

first
Solution

A third-class lever is used to increase distance traveled by an object in the same direction as the force applied. The fulcrum is at one end of the lever, the object at the other, and the force is applied between them. This lever does not impart a mechanical advantage as the effort force must be greater than the load but does impart extra speed to the load. Examples of third-class levers are shovels and tweezers.

3

A wedge is most similar to what other type of simple machine?

70% Answer Correctly

inclined plane

first-class lever

third-class lever

second-class lever
Solution

The wedge is a moving inclined plane that is used to lift, hold, or break apart an object. A wedge converts force applied to its blunt end into force perpendicular to its inclined surface. In contrast to a stationary plane where force is applied to the object being moved, with a wedge the object is stationary and the force is being applied to the plane. Examples of a wedge include knives and chisels.

4

A box is resting on a smooth floor. Static friction is present:

59% Answer Correctly

when an attempt is made to move the box

at all times

only if normal force is present

if the coefficient of friction is greater than one
Solution

For any given surface, the coefficient of static friction is higher than the coefficient of kinetic friction. More force is required to initally get an object moving than is required to keep it moving. Additionally, static friction only arises in response to an attempt to move an object (overcome the normal force between it and the surface).

5 If input effort is 400 ft⋅lb, what output effort will be produced by a machine with a mechanical advantage of 5?
79% Answer Correctly
500ft⋅lb
2000 ft⋅lb
1000ft⋅lb
4000ft⋅lb
Solution
Mechanical advantage is the ratio of output force to input force and tells us by how many times a machine multiplies input effort. So, a machine with a mechanical advantage of 5 will multiply an input effort of 400 ft⋅lb by 5 to produce an output effort of 2000 ft⋅lb.