ASVAB Mechanical Comprehension Practice Test 385757 Results

	Your Results	Global Average
Questions	5	5
Correct	0	2.73
Score	0%	55%

Review

1 What is the efficiency of a machine has work input of 130 ft⋅lb and work output of 65 ft⋅lb?

67% Answer Correctly

	0%
	2%
	200%
	50%

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:
\( Efficiency = \frac{Work_{out}}{Work_{in}} \times 100 \) \( = \frac{65 ft⋅lb}{130 ft⋅lb} \times 100 \) \( = 50% \) %

Which of the following will increase the mechanical advantage of a second-class lever?

55% Answer Correctly

	move the fulcrum between the force and the object being lifted
	decrease the length of the lever
	move the object being lifted farther away from the fulcrum
	move the object being lifted closer to the fulcrum

Solution

A second-class lever is used to increase force on an object in the same direction as the force is applied. This lever requires a smaller force to lift a larger load but the force must be applied over a greater distance. The fulcrum is placed at one end of the lever and mechanical advantage increases as the object being lifted is moved closer to the fulcrum or the length of the lever is increased. An example of a second-class lever is a wheelbarrow.

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

48% Answer Correctly

	counter force
	mass
	friction
	normal force

Solution

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

What type of load varies with time or affects a structure that experiences a high degree of movement?

65% Answer Correctly

	static load
	concentrated load
	dynamic load
	impact load

Solution

A concentrated load acts on a relatively small area of a structure, a static uniformly distributed load doesn't create specific stress points or vary with time, a dynamic load varies with time or affects a structure that experiences a high degree of movement, an impact load is sudden and for a relatively short duration and a non-uniformly distributed load creates different stresses at different locations on a structure.

Force of friction due to kinetic friction is __________ the force of friction due to static friction.

41% Answer Correctly

	lower than
	opposite
	the same as
	higher than

Solution

The formula for force of friction (F_f) is the same whether kinetic or static friction applies: F_{f =}μF_N. To distinguish between kinetic and static friction, μ_k and μ_s are often used in place of μ.