ASVAB Mechanical Comprehension Practice Test 99219 Results

Your Results Global Average
Questions 5 5
Correct 0 3.59
Score 0% 72%

Review

1

Two or more pulleys used together are called:

71% Answer Correctly

wheel and axle

gears

third-class lever

block and tackle
Solution

Two or more pulleys used together constitute a block and tackle which, unlike a fixed pulley, does impart mechanical advantage as a function of the number of pulleys that make up the arrangement.  So, for example, a block and tackle with three pulleys would have a mechanical advantage of three.

2

When all forces acting on a system cancel each other out, this is called:

80% Answer Correctly

rest

equilibrium

potential energy

stasis
Solution

When a system is stable or balanced (equilibrium) all forces acting on the system cancel each other out. In the case of torque, equilibrium means that the sum of the anticlockwise moments about a center of rotation equal the sum of the clockwise moments.

3 What's the mechanical advantage of a wedge that's 4 inches wide and 16 inches long?
83% Answer Correctly
8
12
7
4
Solution

The mechanical advantage (MA) of a wedge is its length divided by its thickness:

MA = \( \frac{l}{t} \) = \( \frac{16 in.}{4 in.} \) = 4

4 If input effort is 600 ft⋅lb, what output effort will be produced by a machine with a mechanical advantage of 6?
79% Answer Correctly
1800ft⋅lb
3600 ft⋅lb
7200ft⋅lb
0ft⋅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 6 will multiply an input effort of 600 ft⋅lb by 6 to produce an output effort of 3600 ft⋅lb.
5 If A = 10 ft., B = 3 ft., C = 9 ft., the green box weighs 30 lbs. and the blue box weighs 35 lbs., what does the orange box have to weigh for this lever to balance?
44% Answer Correctly
10 lbs.
21.67 lbs.
5.42 lbs.
10.83 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:

30 lbs. x 10 ft. = 35 lbs. x 3 ft. + fC x 9 ft.

300 ft. lbs. = 105 ft. lbs. + fC x 9 ft.

fC = \( \frac{300 ft. lbs. - 105 ft. lbs.}{9 ft.} \) = \( \frac{195 ft. lbs.}{9 ft.} \) = 21.67 lbs.