ASVAB Mechanical Comprehension Practice Test 665847 Results

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

Review

1 What is the efficiency of a machine has work input of 50 ft⋅lb and work output of 30 ft⋅lb?

67% Answer Correctly

	60%
	240%
	120%
	0%

Solution

Due to friction, a machine will never be able to utilize 100% of its work input. A certain percentage of that input will be lost in overcoming friction within the machine. Effeciency is a measure of how much of a machine's work input can be turned into useful work output and is calculated by dividing work output by work input and multiplying the result by 100:
\( Efficiency = \frac{Work_{out}}{Work_{in}} \times 100 \) \( = \frac{30 ft⋅lb}{50 ft⋅lb} \times 100 \) \( = 60% \) %

One Horsepower (hp) is equal to how many watts?

76% Answer Correctly

	1
	9.8
	1492
	746

Solution

Power is the rate at which work is done, P = w/t, or work per unit time. The watt (W) is the unit for power and is equal to 1 joule (or newton-meter) per second. Horsepower (hp) is another familiar unit of power used primarily for rating internal combustion engines. 1 hp equals 746 watts.

3 If the force applied at the blue arrow over 8 ft. moves the green box 1.33 ft., what is the mechanical advantage of this lever?

56% Answer Correctly

	6
	9
	5.4
	6.6

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 = \( \frac{8 ft.}{1.33 ft.} \) = 6

You might be wondering how having an effort distance of 6 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 6 times the resistance distance, the effort force must be \( \frac{1}{6} \) the resistance force. You're trading moving 6 times the distance for only having to use \( \frac{1}{6} \) the force.

Which of the following represents the force a surface exerts when an object presses against it?

48% Answer Correctly

	friction
	counter force
	normal force
	mass

Solution

Normal force (F_N) represents the force a surface exerts when an object presses against it.

A truck is using a rope to pull a car. Tension in the rope is greatest in which of the following places?

50% Answer Correctly

	near the car
	in the middle
	tension is equal in all parts of the rope
	near the truck

Solution

Tension is a force that stretches or elongates something. When a cable or rope is used to pull an object, for example, it stretches internally as it accepts the weight that it's moving. Although tension is often treated as applying equally to all parts of a material, it's greater at the places where the material is under the most stress.