ASVAB Mechanical Comprehension Practice Test 350789 Results

	Your Results	Global Average
Questions	5	5
Correct	0	3.66
Score	0%	73%

Review

1 If the green arrow in this diagram represents 180 ft⋅lb of work, how far will the box move if it weighs 90 pounds?

72% Answer Correctly

	45 ft.
	360 ft.
	2 ft.
	1 ft.

Solution

The Law of Work states that the work put into a machine is equal to the work received from the machine under ideal conditions. In equation form, that's:

W_in = W_out
F_effort x d_effort = F_resistance x d_resistance

In this problem, the effort work is 180 ft⋅lb and the resistance force is 90 lbs. and we need to calculate the resistance distance:

W_in = F_resistance x d_resistance
180 ft⋅lb = 90 lbs. x d_resistance
d_resistance = \( \frac{180ft⋅lb}{90 lbs.} \) = 2 ft.

The mechanical advantage of connected gears is proportional to which characteristic of the gears?

73% Answer Correctly

	speed
	circumference
	number of teeth
	diameter

Solution

The mechanical advantage (amount of change in speed or torque) of connected gears is proportional to the number of teeth each gear has. Called gear ratio, it's the ratio of the number of teeth on the larger gear to the number of teeth on the smaller gear. For example, a gear with 12 teeth connected to a gear with 9 teeth would have a gear ratio of 4:3.

A fixed pulley has a mechanical advantage of:

68% Answer Correctly

	-1
	2
	0
	1

Solution

A fixed pulley is used to change the direction of a force and does not multiply the force applied. As such, it has a mechanical advantage of one. The benefit of a fixed pulley is that it can allow the force to be applied at a more convenient angle, for example, pulling downward or horizontally to lift an object instead of upward.

The force required to initally get an object moving is __________ the force required to keep it moving.

76% Answer Correctly

	higher than
	lower than
	the same as
	opposite

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).

5 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

	5
	10
	11
	4.5

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