ASVAB Mechanical Comprehension Practice Test 507769 Results

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

Review

The mechanical advantage of a wheel and axle is equal to the:

61% Answer Correctly

	ratio of the diameters of the wheels
	length of the axle
	difference in the lengths of the axles
	difference in the diameters of the wheels

Solution

A wheel and axle uses two different diameter wheels mounted to a connecting axle. Force is applied to the larger wheel and large movements of this wheel result in small movements in the smaller wheel. Because a larger movement distance is being translated to a smaller distance, force is increased with a mechanical advantage equal to the ratio of the diameters of the wheels. An example of a wheel and axle is the steering wheel of a car.

2 What is the efficiency of a machine has work input of 110 ft⋅lb and work output of 88 ft⋅lb?

67% Answer Correctly

	1%
	0%
	80%
	160%

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:
\( Efficiency = \frac{Work_{out}}{Work_{in}} \times 100 \) \( = \frac{88 ft⋅lb}{110 ft⋅lb} \times 100 \) \( = 80% \) %

Sam can do 50 ft. lb. of work in 2 minutes and 5 seconds. What would Sam have to do to increase his power output?

64% Answer Correctly

	do the work in 2 minutes
	do the work in 3 minutes
	do 25 ft. lb. of work in 2 minutes 5 seconds
	do 100 ft. lb. of work in 4 minutes 12 seconds

Solution

Power is the rate of doing work or \(\frac{W}{t}\). To increase power, increase the work being done in the same amount of time or do the same amount of work in less time.

Collinear forces:

72% Answer Correctly

	act in a common plane
	act along the same line of action
	pass through a common point
	are unrelated to each other

Solution

Collinear forces act along the same line of action, concurrent forces pass through a common point and coplanar forces act in a common plane.

What defines the mechanical advantage of a first class lever?

65% Answer Correctly

	input force
	output distance
	output force
	position of the fulcrum

Solution

A first-class lever is used to increase force or distance while changing the direction of the force. The lever pivots on a fulcrum and, when a force is applied to the lever at one side of the fulcrum, the other end moves in the opposite direction. The position of the fulcrum also defines the mechanical advantage of the lever. If the fulcrum is closer to the force being applied, the load can be moved a greater distance at the expense of requiring a greater input force. If the fulcrum is closer to the load, less force is required but the force must be applied over a longer distance. An example of a first-class lever is a seesaw / teeter-totter.