ASVAB Mechanical Comprehension Practice Test 885892 Results

	Your Results	Global Average
Questions	5	5
Correct	0	2.80
Score	0%	56%

Review

Which class of lever offers no mechanical advantage?

45% Answer Correctly

	first
	none of these, all levers offer mechanical advantage
	second
	third

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.

2 If A = 4 ft. and the green box weighs 10 lbs. what is the torque acting on the A side of this lever?

75% Answer Correctly

	10 ft⋅lb
	2 ft⋅lb
	20 ft⋅lb
	40 ft⋅lb

Solution

For a lever, torque is weight x distance from the fulcrum which, in this case, is: 10 ft. x 4 lbs. = 40 ft⋅lb

Which of the following is not true of a first-class lever?

51% Answer Correctly

	increases distance
	decreases distance
	increases force
	changes the direction of force

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.

4 If the green box weighs 10 lbs. and is 5 ft. from the fulcrum, how far from the fulcrum would a 70 lbs. force need to be applied to balance the lever?

58% Answer Correctly

	0.36 ft.
	50 ft.
	2.14 ft.
	0.71 ft.

Solution

To balance this lever the torques at the green box and the blue arrow must be equal. Torque is weight x distance from the fulcrum so the equation for equilibrium is:

R_ad_a = R_bd_b

where a represents the green box and b the blue arrow, R is resistance (weight/force) and d is the distance from the fulcrum.

Solving for d_b, our missing value, and plugging in our variables yields:

d_b = \( \frac{R_ad_a}{R_b} \) = \( \frac{10 lbs. \times 5 ft.}{70 lbs.} \) = \( \frac{50 ft⋅lb}{70 lbs.} \) = 0.71 ft.

A screw is most like which of the following other simple machines?

50% Answer Correctly

	first-class lever
	inclined plane
	wheel and axle
	block and tackle

Solution

A screw is an inclined plane wrapped in ridges (threads) around a cylinder. The distance between these ridges defines the pitch of the screw and this distance is how far the screw advances when it is turned once. The mechanical advantage of a screw is its circumference divided by the pitch.