ASVAB Mechanical Comprehension Practice Test 173721 Results

Your Results Global Average
Questions 5 5
Correct 0 2.96
Score 0% 59%

Review

1 If A = 8 ft., B = 2 ft., C = 4 ft., the green box weighs 45 lbs. and the blue box weighs 65 lbs., what does the orange box have to weigh for this lever to balance?
44% Answer Correctly
115 lbs.
360 lbs.
57.5 lbs.
5 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:

45 lbs. x 8 ft. = 65 lbs. x 2 ft. + fC x 4 ft.

360 ft. lbs. = 130 ft. lbs. + fC x 4 ft.

fC = \( \frac{360 ft. lbs. - 130 ft. lbs.}{4 ft.} \) = \( \frac{230 ft. lbs.}{4 ft.} \) = 57.5 lbs.

2

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

increasing the coefficient of friction

moving the object farther

moving the object with more speed
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.

3 What is the efficiency of a machine has work input of 70 ft⋅lb and work output of 31 ft⋅lb?
67% Answer Correctly
45%
55%
90%
11%
Solution
Due to friction, a machine will never be able to utilize 100% of its work input. A certain percentage of that input will be lost in overcoming friction within the machine. Effeciency is a measure of how much of a machine's work input can be turned into useful work output and is calculated by dividing work output by work input and multiplying the result by 100:
\( Efficiency = \frac{Work_{out}}{Work_{in}} \times 100 \) \( = \frac{31 ft⋅lb}{70 ft⋅lb} \times 100 \) \( = 45% \) %
4

A fixed pulley is useful for which of the following?

54% Answer Correctly

changing the direction of the input force

multiplying the input force

changing the direction of the output force

multiplying the input distance
Solution

A fixed pulley is used to change the direction of a force and does not multiply the force applied. As such, it has a mechanical advantage of one. The benefit of a fixed pulley is that it can allow the force to be applied at a more convenient angle, for example, pulling downward or horizontally to lift an object instead of upward.

5

The force required to initally get an object moving is __________ the force required to keep it moving. 

76% Answer Correctly

the same as

lower than

higher than

opposite
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).