ASVAB Mechanical Comprehension Practice Test 835651 Results

	Your Results	Global Average
Questions	5	5
Correct	0	2.95
Score	0%	59%

Review

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

40% Answer Correctly

	opposite
	higher than
	the same as
	lower 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.

Friction resists movement in a direction __________ to the movement.

81% Answer Correctly

	opposite
	perpendicular
	normal
	parallel

Solution

Friction resists movement. Kinetic (also called sliding or dynamic) friction resists movement in a direction opposite to the movement. Because it opposes movement, kinetic friction will eventually bring an object to a stop. An example is a rock that's sliding across ice.

3 If you have a gear train with three gears, the first with 30 teeth, the second with 14 teeth, and the third with 8 teeth, what is its mechanical advantage?

51% Answer Correctly

	3.8
	7.5
	5.6
	5.8

Solution

The mechanical advantage of a gear train is its gear ratio. The gear ratio (V_r) 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 three gears so the equation becomes:

V_r = \( \frac{N_1}{N_2} \) \( \frac{N_2}{N_3} \) = \( \frac{30}{14} \) \( \frac{14}{8} \) = \( \frac{30}{8} \) = 3.8

4 If A = 1 ft. and the green box weighs 35 lbs. what is the torque acting on the A side of this lever?

75% Answer Correctly

	140 ft⋅lb
	35 ft⋅lb
	11 ft⋅lb
	17 ft⋅lb

Solution

For a lever, torque is weight x distance from the fulcrum which, in this case, is: 35 ft. x 1 lbs. = 35 ft⋅lb

Which class of lever offers no mechanical advantage?

45% Answer Correctly

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

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.