ASVAB Mechanical Comprehension Practice Test 720629 Results

	Your Results	Global Average
Questions	5	5
Correct	0	3.35
Score	0%	67%

Review

1 If A = 9 ft. and the green box weighs 15 lbs. what is the torque acting on the A side of this lever?

74% Answer Correctly

	270 ft⋅lb
	135 ft⋅lb
	0 ft⋅lb
	540 ft⋅lb

Solution

For a lever, torque is weight x distance from the fulcrum which, in this case, is: 15 ft. x 9 lbs. = 135 ft⋅lb

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

51% Answer Correctly

	changes the direction of force
	increases force
	increases distance
	decreases distance

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.

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

60% Answer Correctly

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

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).

4 If you have a gear train with two gears, the first with 20 teeth and the second with 4 teeth, how many revolutions does the second gear make for each revolution of the first gear?

77% Answer Correctly

	-3
	8
	2.5
	5

Solution

The gear ratio (V_r) of a gear train is the product of the gear ratios between the pairs of meshed gears. Let N represent the number of teeth for each gear:

V_r = \( \frac{N_1}{N_2} \) \( \frac{N_2}{N_3} \) \( \frac{N_3}{N_4} \) ... \( \frac{N_n}{N_{n+1}} \)

In this problem, we have only two gears so the equation becomes:

V_r = \( \frac{N_1}{N_2} \) = \( \frac{20}{4} \) = 5

Collinear forces:

72% Answer Correctly

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

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.