ASVAB Mechanical Comprehension Practice Test 90507 Results

	Your Results	Global Average
Questions	5	5
Correct	0	2.91
Score	0%	58%

Review

1 If you lift a 10 lbs. rock 31 ft. from the ground, how much work have you done?

71% Answer Correctly

	310 ft⋅lb
	0 ft⋅lb
	620 ft⋅lb
	41 ft⋅lb

Solution

Work is force times distance. In this case, the force is the weight of the rock so:
\( W = F \times d \)
\( W = 10 \times 31 \)
\( W = 310 \)

Which of the following is the formula for torque?

61% Answer Correctly

	τ = F/r
	τ = rF
	τ = F/r²
	τ = r/F

Solution

Torque measures force applied during rotation: τ = rF. Torque (τ, the Greek letter tau) = the radius of the lever arm (r) multiplied by the force (F) applied. Radius is measured from the center of rotation or fulcrum to the point at which the perpendicular force is being applied. The resulting unit for torque is newton-meter (N-m) or foot-pound (ft-lb).

Power is the rate at which:

62% Answer Correctly

	input force is transferred to output force
	work is done
	potential energy is converted into kinetic energy
	friction is overcome

Solution

Power is the rate at which work is done, P = w/t, or work per unit time. The watt (W) is the unit for power and is equal to 1 joule (or newton-meter) per second. Horsepower (hp) is another familiar unit of power used primarily for rating internal combustion engines. 1 hp equals 746 watts.

The principle of conservation of mechanical energy states that, as long as no other forces are applied, what will remain constant as an object falls?

45% Answer Correctly

	total mechanical energy
	acceleration
	potential energy
	kinetic energy

Solution

As an object falls, its potential energy is converted into kinetic energy. The principle of conservation of mechanical energy states that, as long as no other forces are applied, total mechanical energy (PE + KE) of the object will remain constant at all points in its descent.

5 The radius of the axle is 7, the radius of the wheel is 10, and the blue box weighs 65 lbs. What is the effort force necessary to balance the load?

53% Answer Correctly

	17 lbs.
	14.3 lbs.
	11.43 lbs.
	45.45 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 7 for a mechanical advantage of \( \frac{10}{7} \) = 1.43

MA = \( \frac{load}{effort} \) so effort = \( \frac{load}{MA} \) = \( \frac{65 lbs.}{1.43} \) = 45.45 lbs.