ASVAB Mechanical Comprehension Practice Test 15924 Results

Your Results Global Average
Questions 5 5
Correct 0 2.88
Score 0% 58%

Review

1

Friction between two or more solid objects that are not moving relative to each other is called:

73% Answer Correctly

gravitational friction

kinetic friction

dynamic friction

static friction
Solution

Static friction is friction between two or more solid objects that are not moving relative to each other. An example is the friction that prevents a box on a sloped surface from sliding farther down the surface.

2

The mechanical advantage of a wheel and axle is equal to the:

61% Answer Correctly

length of the axle

difference in the lengths of the axles

difference in the diameters of the wheels

ratio of the diameters of the wheels
Solution

A wheel and axle uses two different diameter wheels mounted to a connecting axle. Force is applied to the larger wheel and large movements of this wheel result in small movements in the smaller wheel. Because a larger movement distance is being translated to a smaller distance, force is increased with a mechanical advantage equal to the ratio of the diameters of the wheels. An example of a wheel and axle is the steering wheel of a car.

3 What is the power output of a 5 hp engine that's 80% efficient?
40% Answer Correctly
2200 \( \frac{ft⋅lb}{s} \)
8800 \( \frac{ft⋅lb}{s} \)
733.3 \( \frac{ft⋅lb}{s} \)
1100 \( \frac{ft⋅lb}{s} \)
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 5 hp x 550 \( \frac{ft⋅lb}{s} \) = 2750 \( \frac{ft⋅lb}{s} \)
\( P_{o} = \frac{E \times P_{i}}{100} = \frac{80 \times 2750 \frac{ft⋅lb}{s}}{100} \) \( = \frac{220000 \frac{ft⋅lb}{s}}{100} \) = 2200 \( \frac{ft⋅lb}{s} \)
4

Which of the following is the formula for hydraulic pressure?

58% Answer Correctly

P = F/A

P = F/A2

P = FA2

P = FA
Solution

Hydraulics is the transmission of force through the use of liquids. Liquids are especially suited for transferring force in complex machines because they compress very little and can occupy very small spaces. Hydraulic pressure is calculated by dividing force by the area over which it is applied: P = F/A where F is force in pounds, A is area in square inches, and the resulting pressure is in pounds per square inch (psi).

5 The radius of the axle is 5, the radius of the wheel is 6, and the blue box weighs 45 lbs. What is the effort force necessary to balance the load?
53% Answer Correctly
11 lbs.
6 lbs.
7.2 lbs.
37.5 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 6 and the output radius (where the resistance is being applied) is 5 for a mechanical advantage of \( \frac{6}{5} \) = 1.2

MA = \( \frac{load}{effort} \) so effort = \( \frac{load}{MA} \) = \( \frac{45 lbs.}{1.2} \) = 37.5 lbs.