ASVAB Mechanical Comprehension Practice Test 854226 Results

Your Results Global Average
Questions 5 5
Correct 0 2.65
Score 0% 53%

Review

1 If A = 1 ft. and the green box weighs 25 lbs. what is the torque acting on the A side of this lever?
74% Answer Correctly
25 ft⋅lb
75 ft⋅lb
8 ft⋅lb
12 ft⋅lb
Solution
For a lever, torque is weight x distance from the fulcrum which, in this case, is: 25 ft. x 1 lbs. = 25 ft⋅lb
2 What is the power output of a 8 hp engine that's 90% efficient?
40% Answer Correctly
0 \( \frac{ft⋅lb}{s} \)
990 \( \frac{ft⋅lb}{s} \)
11880 \( \frac{ft⋅lb}{s} \)
3960 \( \frac{ft⋅lb}{s} \)
Solution
\( Efficiency = \frac{Power_{out}}{Power_{in}} \times 100 \)
Solving for power out: \( P_{o} = \frac{E \times P_{i}}{100} \)
Knowing that 1 hp = 550 \( \frac{ft⋅lb}{s} \), Pi becomes 8 hp x 550 \( \frac{ft⋅lb}{s} \) = 4400 \( \frac{ft⋅lb}{s} \)
\( P_{o} = \frac{E \times P_{i}}{100} = \frac{90 \times 4400 \frac{ft⋅lb}{s}}{100} \) \( = \frac{396000 \frac{ft⋅lb}{s}}{100} \) = 3960 \( \frac{ft⋅lb}{s} \)
3 If the radius of the axle is 7 and the radius of the wheel is 12, what is the mechanical advantage of this wheel and axle configuration?
36% Answer Correctly
-5
1
0
5
Solution

The mechanical advantage of a wheel and axle lies in the difference in radius between the inner (axle) wheel and the outer wheel. But, this mechanical advantage is only realized when the input effort and load are applied to different wheels. Applying both input effort and load to the same wheel results in a mechanical advantage of 1.

4

Concurrent forces:

55% Answer Correctly

act in a common dimension

act along the same line of action

pass through a common point

act in a common plane
Solution

Collinear forces act along the same line of action, concurrent forces pass through a common point and coplanar forces act in a common plane.

5 If the green box weighs 25 lbs. and is 9 ft. from the fulcrum, how far from the fulcrum would a 60 lbs. force need to be applied to balance the lever?
58% Answer Correctly
11.25 ft.
3.75 ft.
1.25 ft.
1.88 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 = \( \frac{R_ad_a}{R_b} \) = \( \frac{25 lbs. \times 9 ft.}{60 lbs.} \) = \( \frac{225 ft⋅lb}{60 lbs.} \) = 3.75 ft.