ASVAB Mechanical Comprehension Practice Test 486654 Results

	Your Results	Global Average
Questions	5	5
Correct	0	3.28
Score	0%	66%

Review

1 If you lift a 24 lbs. rock 35 ft. from the ground, how much work have you done?

70% Answer Correctly

	1680 ft⋅lb
	59 ft⋅lb
	1 ft⋅lb
	840 ft⋅lb

Solution

Work is force times distance. In this case, the force is the weight of the rock so:
\( W = F \times d \)
\( W = 24 \times 35 \)
\( W = 840 \)

When all forces acting on a system cancel each other out, this is called:

80% Answer Correctly

	equilibrium
	rest
	stasis
	potential energy

Solution

When a system is stable or balanced (equilibrium) all forces acting on the system cancel each other out. In the case of torque, equilibrium means that the sum of the anticlockwise moments about a center of rotation equal the sum of the clockwise moments.

3 If this lever is in equilibrium with an effort force of 20.0 ft. lb. at the blue arrow and a resistance force of 8 ft. lb. at the green box, what is its mechanical advantage?

48% Answer Correctly

	0.13
	0.4
	2.4
	0.36

Solution

Mechanical advantage (MA) is the ratio by which effort force relates to resistance force. If both forces are known, calculating MA is simply a matter of dividing resistance force by effort force:

MA = \( \frac{F_r}{F_e} \) = \( \frac{8 ft.}{20.0 ft.} \) = 0.4

In this case, the mechanical advantage is less than one meaning that each unit of effort force results in just 0.4 units of resistance force. However, a third class lever like this isn't designed to multiply force like a first class lever. A third class lever is designed to multiply distance and speed at the resistance by sacrificing force at the resistance. Different lever styles have different purposes and multiply forces in different ways.

Which of the following represents the force a surface exerts when an object presses against it?

48% Answer Correctly

	friction
	counter force
	mass
	normal force

Solution

Normal force (F_N) represents the force a surface exerts when an object presses against it.

Drag is a type of:

81% Answer Correctly

	potential energy
	kinetic energy
	friction
	work

Solution

Drag is friction that opposes movement through a fluid like liquid or air. The amount of drag depends on the shape and speed of the object with slower objects experiencing less drag than faster objects and more aerodynamic objects experiencing less drag than those with a large leading surface area.