ASVAB Mechanical Comprehension Practice Test 561460 Results

	Your Results	Global Average
Questions	5	5
Correct	0	3.65
Score	0%	73%

Review

What is work?

60% Answer Correctly

	The movement of an object by a force
	The potential for exertion
	Force per unit distance
	Force per unit time

Solution

Work is accomplished when force is applied to an object: W = Fd where F is force in newtons (N) and d is distance in meters (m). Thus, the more force that must be applied to move an object, the more work is done and the farther an object is moved by exerting force, the more work is done. By definition, work is the displacement of an object resulting from applied force.

2 If you have a gear train with two gears, the first with 36 teeth and the second with 4 teeth, how many revolutions does the second gear make for each revolution of the first gear?

78% Answer Correctly

	4.5
	9
	12
	3

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 = \( \frac{N_1}{N_2} \) = \( \frac{36}{4} \) = 9

The force amplification achieved by using a tool, mechanical device or machine system is called:

80% Answer Correctly

	efficiency
	work
	mechanical advantage
	power

Solution

Mechanical advantage is a measure of the force amplification achieved by using a tool, mechanical device or machine system. Such a device utilizes input force and trades off forces against movement to amplify and/or change its direction.

4 If you lift a 25 lbs. rock 13 ft. from the ground, how much work have you done?

71% Answer Correctly

	None of these is correct
	325 ft⋅lb
	38 ft⋅lb
	650 ft⋅lb

Solution

Work is force times distance. In this case, the force is the weight of the rock so:
\( W = F \times d \)
\( W = 25 \times 13 \)
\( W = 325 \)

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

76% Answer Correctly

	opposite
	lower than
	higher than
	the same as

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).