ASVAB Mechanical Comprehension Practice Test 826226 Results

	Your Results	Global Average
Questions	5	5
Correct	0	3.01
Score	0%	60%

Review

The measure of how much of the power put into a machine is turned into movement or force is called:

56% Answer Correctly

	power
	efficiency
	mechanical advantage
	force multiplication

Solution

The efficiency of a machine describes how much of the power put into the machine is turned into movement or force. A 100% efficient machine would turn all of the input power into output movement or force. However, no machine is 100% efficient due to friction, heat, wear and other imperfections that consume input power without delivering any output.

When it comes to force, mass and acceleration have what kind of relationship?

66% Answer Correctly

	exponential
	logarithmic
	linear
	inverse

Solution

Newton's Second Law of Motion states that "The acceleration of an object as produced by a net force is directly proportional to the magnitude of the net force, in the same direction as the net force, and inversely proportional to the mass of the object." This Law describes the linear relationship between mass and acceleration when it comes to force and leads to the formula F = ma or force equals mass multiplied by rate of acceleration.

What's the first gear in a gear train called?

57% Answer Correctly

	idler gear
	driver gear
	input gear
	driven gear

Solution

A gear train is two or more gears linked together. Gear trains are designed to increase or reduce the speed or torque outpout of a rotating system or change the direction of its output. The first gear in the chain is called the driver and the last gear in the chain the driven gear with the gears between them called idler gears.

4 A = 7 ft., the green box weighs 25 lbs., and the blue box weighs 65 lbs. What does distance B need to be for this lever to balance?

65% Answer Correctly

	10.77 ft.
	2.69 ft.
	0.9 ft.
	175 ft.

Solution

In order for this lever to balance, the torque acting on side A must equal the torque acting on side B. Torque is weight x distance from the fulcrum which means that the following must be true for the lever to balance:

f_Ad_A = f_Bd_B

For this problem, the equation becomes:

25 lbs. x 7 ft. = 65 lbs. x d_B

d_B = \( \frac{25 \times 7 ft⋅lb}{65 lbs.} \) = \( \frac{175 ft⋅lb}{65 lbs.} \) = 2.69 ft.

5 If the force applied at the blue arrow over 7 ft. moves the green box 2.33 ft., what is the mechanical advantage of this lever?

56% Answer Correctly

	9
	3.3
	3
	6

Solution

Mechanical advantage (MA) can be calculated knowing only the distance the effort (blue arrow) moves and the distance the resistance (green box) moves. The equation is:

MA = \( \frac{E_d}{R_d} \)

where E_d is the effort distance and R_d is the resistance distance. For this problem, the equation becomes:

MA = \( \frac{7 ft.}{2.33 ft.} \) = 3

You might be wondering how having an effort distance of 3 times the resistance distance is an advantage. Remember the principle of moments. For a lever in equilibrium the effort torque equals the resistance torque. Because torque is force x distance, if the effort distance is 3 times the resistance distance, the effort force must be \( \frac{1}{3} \) the resistance force. You're trading moving 3 times the distance for only having to use \( \frac{1}{3} \) the force.