ASVAB Mechanical Comprehension Practice Test 166729 Results

	Your Results	Global Average
Questions	5	5
Correct	0	2.98
Score	0%	60%

Review

1 What is the efficiency of a machine has work input of 85 ft⋅lb and work output of 68 ft⋅lb?

67% Answer Correctly

	320%
	80%
	20%
	1%

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:
\( Efficiency = \frac{Work_{out}}{Work_{in}} \times 100 \) \( = \frac{68 ft⋅lb}{85 ft⋅lb} \times 100 \) \( = 80% \) %

The advantage of using a third-class lever is that it increases:

37% Answer Correctly

	the speed of the load
	the mechanical advantage of the lever
	the force applied to the load
	the distance traveled by the load

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.

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

66% Answer Correctly

	impact load
	dynamic load
	concentrated load
	static 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.

4 What's the mechanical advantage of a wedge that's 5 inches wide and 15 inches long?

83% Answer Correctly

	3
	-3
	5
	6

Solution

The mechanical advantage (MA) of a wedge is its length divided by its thickness:

MA = \( \frac{l}{t} \) = \( \frac{15 in.}{5 in.} \) = 3

Which of the following statements about this pulley configuration is false?

48% Answer Correctly

	Mechanical advantage is the number of ropes that support the resistance
	Changes the direction of and multiplies the effort force
	Only multiplies the effort force
	This is a block and tackle pulley configuration

Solution

A block and tackle is a combination of one or more fixed pulleys and one or more movable pulleys where the fixed pulleys change the direction of the effort force and the movable pulleys multiply it. The mechanical advantage is equal to the number of times the effort force changes direction and can be increased by adding more pulley wheels to the system. An easy way to find the mechanical advantage of a block and tackle pulley system is to count the number of ropes that support the resistance.