ASVAB Mechanical Comprehension Practice Test 210463 Results

	Your Results	Global Average
Questions	5	5
Correct	0	3.20
Score	0%	64%

Review

A screw is most like which of the following other simple machines?

50% Answer Correctly

	wheel and axle
	inclined plane
	block and tackle
	first-class lever

Solution

A screw is an inclined plane wrapped in ridges (threads) around a cylinder. The distance between these ridges defines the pitch of the screw and this distance is how far the screw advances when it is turned once. The mechanical advantage of a screw is its circumference divided by the pitch.

2 If the force applied at the blue arrow over 9 ft. moves the green box 1.29 ft., what is the mechanical advantage of this lever?

56% Answer Correctly

	21
	10.5
	7
	14

Solution

Mechanical advantage (MA) can be calculated knowing only the distance the effort (blue arrow) moves and the distance the resistance (green box) moves. The equation is:

MA = \( \frac{E_d}{R_d} \)

where E_d is the effort distance and R_d is the resistance distance. For this problem, the equation becomes:

MA = \( \frac{9 ft.}{1.29 ft.} \) = 7

You might be wondering how having an effort distance of 7 times the resistance distance is an advantage. Remember the principle of moments. For a lever in equilibrium the effort torque equals the resistance torque. Because torque is force x distance, if the effort distance is 7 times the resistance distance, the effort force must be \( \frac{1}{7} \) the resistance force. You're trading moving 7 times the distance for only having to use \( \frac{1}{7} \) the force.

Potential energy is energy that has the potential to be converted into what?

80% Answer Correctly

	kinetic energy
	work
	power
	heat

Solution

Potential energy is the energy of an object by virtue of its position relative to other objects. It is energy that has the potential to be converted into kinetic energy.

Which of the following is the formula for torque?

61% Answer Correctly

	τ = F/r
	τ = r/F
	τ = rF
	τ = F/r²

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).

5 If the green arrow in this diagram represents 300 ft⋅lb of work, how far will the box move if it weighs 150 pounds?

72% Answer Correctly

	4 ft.
	300 ft.
	2 ft.
	37 ft.

Solution

The Law of Work states that the work put into a machine is equal to the work received from the machine under ideal conditions. In equation form, that's:

W_in = W_out
F_effort x d_effort = F_resistance x d_resistance

In this problem, the effort work is 300 ft⋅lb and the resistance force is 150 lbs. and we need to calculate the resistance distance:

W_in = F_resistance x d_resistance
300 ft⋅lb = 150 lbs. x d_resistance
d_resistance = \( \frac{300ft⋅lb}{150 lbs.} \) = 2 ft.