ASVAB Mechanical Comprehension Practice Test 747567 Results

Your Results Global Average
Questions 5 5
Correct 0 3.14
Score 0% 63%

Review

1 If A = 9 ft., B = 2 ft., C = 7 ft., the green box weighs 50 lbs. and the blue box weighs 60 lbs., what does the orange box have to weigh for this lever to balance?
43% Answer Correctly
47.14 lbs.
25 lbs.
0 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:

50 lbs. x 9 ft. = 60 lbs. x 2 ft. + fC x 7 ft.

450 ft. lbs. = 120 ft. lbs. + fC x 7 ft.

fC = \( \frac{450 ft. lbs. - 120 ft. lbs.}{7 ft.} \) = \( \frac{330 ft. lbs.}{7 ft.} \) = 47.14 lbs.

2

What is the first step to solving a problem where multiple forces are acting on an object?

61% Answer Correctly

calculate potential energy

calculate the net force

calculate the total force

calculate kinetic energy
Solution

In mechanics, multiple forces are often acting on a particular object and, taken together, produce the net force acting on that object. Like force, net force is a vector quantity in that it has magnitude and direction.

3

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

76% Answer Correctly

lower than

higher than

opposite

the same as
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).

4 If input effort is 300 ft⋅lb, what output effort will be produced by a machine with a mechanical advantage of 8?
79% Answer Correctly
0ft⋅lb
37ft⋅lb
4800ft⋅lb
2400 ft⋅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 8 will multiply an input effort of 300 ft⋅lb by 8 to produce an output effort of 2400 ft⋅lb.
5 The radius of the axle is 5, the radius of the wheel is 10, and the blue box weighs 50 lbs. What is the effort force necessary to balance the load?
53% Answer Correctly
7 lbs.
12 lbs.
25 lbs.
15 lbs.
Solution

The mechanical advantage of a wheel and axle is the input radius divided by the output radius:

MA = \( \frac{r_i}{r_o} \)

In this case, the input radius (where the effort force is being applied) is 10 and the output radius (where the resistance is being applied) is 5 for a mechanical advantage of \( \frac{10}{5} \) = 2.0

MA = \( \frac{load}{effort} \) so effort = \( \frac{load}{MA} \) = \( \frac{50 lbs.}{2.0} \) = 25 lbs.