ASVAB Mechanical Comprehension Practice Test 873987 Results

	Your Results	Global Average
Questions	5	5
Correct	0	3.29
Score	0%	66%

Review

Which of the following is the formula for torque?

62% Answer Correctly

	τ = r/F
	τ = F/r²
	τ = F/r
	τ = rF

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).

2 What is the efficiency of a machine has work input of 60 ft⋅lb and work output of 39 ft⋅lb?

67% Answer Correctly

	32%
	16%
	1%
	65%

Solution

Due to friction, a machine will never be able to utilize 100% of its work input. A certain percentage of that input will be lost in overcoming friction within the machine. Effeciency is a measure of how much of a machine's work input can be turned into useful work output and is calculated by dividing work output by work input and multiplying the result by 100:
\( Efficiency = \frac{Work_{out}}{Work_{in}} \times 100 \) \( = \frac{39 ft⋅lb}{60 ft⋅lb} \times 100 \) \( = 65% \) %

A box is resting on a smooth floor. Static friction is present:

59% Answer Correctly

	if the coefficient of friction is greater than one
	when an attempt is made to move the box
	at all times
	only if normal force is present

Solution

For any given surface, the coefficient of static friction is higher than the coefficient of kinetic friction. More force is required to initally get an object moving than is required to keep it moving. Additionally, static friction only arises in response to an attempt to move an object (overcome the normal force between it and the surface).

A ramp is an example of which kind of simple machine?

85% Answer Correctly

	first-class lever
	none of these
	inclined plane
	wedge

Solution

An inclined plane is a simple machine that reduces the force needed to raise an object to a certain height. Work equals force x distance and, by increasing the distance that the object travels, an inclined plane reduces the force necessary to raise it to a particular height. In this case, the mechanical advantage is to make the task easier. An example of an inclined plane is a ramp.

A shovel is an example of which class of lever?

56% Answer Correctly

	third
	a shovel is not a lever
	first
	second

Solution

A third-class lever is used to increase distance traveled by an object in the same direction as the force applied. The fulcrum is at one end of the lever, the object at the other, and the force is applied between them. This lever does not impart a mechanical advantage as the effort force must be greater than the load but does impart extra speed to the load. Examples of third-class levers are shovels and tweezers.