ASVAB Mechanical Comprehension Practice Test 229599 Results

	Your Results	Global Average
Questions	5	5
Correct	0	3.05
Score	0%	61%

Review

1 If you have a gear train with two gears, the first with 28 teeth and the second with 12 teeth, how many revolutions does the second gear make for each revolution of the first gear?

77% Answer Correctly

	4.3
	4.7
	2.1
	2.3

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 = \( \frac{N_1}{N_2} \) = \( \frac{28}{12} \) = 2.3

2 How much work can a 4 hp engine do in 4 seconds?

52% Answer Correctly

	1 ft⋅lb
	8800 ft⋅lb
	2 ft⋅lb
	8 ft⋅lb

Solution

Horsepower (hp) is a common measure of power output for complex machines. By definition, a 1 hp machine does 550 ft⋅lb of work in 1 second: 1 hp = 550 ft⋅lb/s. Substituting the variables for this problem gives us:
\( W = 4 hp \times 550 \frac{ft⋅lb}{s} \times 4s = 8800 ft⋅lb \)

Sam can do 50 ft. lb. of work in 2 minutes and 5 seconds. What would Sam have to do to increase his power output?

64% Answer Correctly

	do the work in 3 minutes
	do 100 ft. lb. of work in 4 minutes 12 seconds
	do 25 ft. lb. of work in 2 minutes 5 seconds
	do the work in 2 minutes

Solution

Power is the rate of doing work or \(\frac{W}{t}\). To increase power, increase the work being done in the same amount of time or do the same amount of work in less time.

Which of the following statements about drag is false?

58% Answer Correctly

	the amount of drag depends on the shape of an object
	drag occurs during movement through a fluid
	the amount of drag depends on the speed of an object
	slower objects experience more drag than faster objects

Solution

Drag is friction that opposes movement through a fluid like liquid or air. The amount of drag depends on the shape and speed of the object with slower objects experiencing less drag than faster objects and more aerodynamic objects experiencing less drag than those with a large leading surface area.

Torque involves a perpendicular force applied to a lever arm that moves around a center of rotation. Increasing the length of the lever arm will do which of the following?

54% Answer Correctly

	increase applied force
	increase torque
	decrease torque
	decrease applied force

Solution

Torque measures force applied during rotation: τ = rF. Torque (τ, the Greek letter tau) = the radius of the lever arm (r) multiplied by the force (F) applied. Radius is measured from the center of rotation or fulcrum to the point at which the perpendicular force is being applied. The resulting unit for torque is newton-meter (N-m) or foot-pound (ft-lb).