ASVAB Mechanical Comprehension Practice Test 708001 Results

	Your Results	Global Average
Questions	5	5
Correct	0	2.93
Score	0%	59%

Review

What type of load varies with time or affects a structure that experiences a high degree of movement?

66% Answer Correctly

	impact load
	dynamic load
	static load
	concentrated load

Solution

A concentrated load acts on a relatively small area of a structure, a static uniformly distributed load doesn't create specific stress points or vary with time, a dynamic load varies with time or affects a structure that experiences a high degree of movement, an impact load is sudden and for a relatively short duration and a non-uniformly distributed load creates different stresses at different locations on a structure.

Which class of lever is used to increase force on an object in the same direction as the force is applied?

53% Answer Correctly

	second
	first
	all of these
	third

Solution

A second-class lever is used to increase force on an object in the same direction as the force is applied. This lever requires a smaller force to lift a larger load but the force must be applied over a greater distance. The fulcrum is placed at one end of the lever and mechanical advantage increases as the object being lifted is moved closer to the fulcrum or the length of the lever is increased. An example of a second-class lever is a wheelbarrow.

3 If the force applied at the blue arrow over 3 ft. moves the green box 1.0 ft., what is the mechanical advantage of this lever?

56% Answer Correctly

	4.5
	1
	3
	3.3

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 = \( \frac{3 ft.}{1.0 ft.} \) = 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.

Power is the rate at which:

63% Answer Correctly

	friction is overcome
	work is done
	input force is transferred to output force
	potential energy is converted into kinetic energy

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.

5 If the green box weighs 30 lbs. and 50 lbs. of force is applied 1 ft. from the fulcrum at the blue arrow, how far from the fulcrum would the green box need to be placed to balance the lever?

55% Answer Correctly

	5 ft.
	0.83 ft.
	30 ft.
	1.67 ft.

Solution

To balance this lever the torques at the green box and the blue arrow must be equal. Torque is weight x distance from the fulcrum so the equation for equilibrium is:

R_ad_a = R_bd_b

where a represents the green box and b the blue arrow, R is resistance (weight/force) and d is the distance from the fulcrum.

Solving for d_a, our missing value, and plugging in our variables yields:

d_a = \( \frac{R_bd_b}{R_a} \) = \( \frac{50 lbs. \times 1 ft.}{30 lbs.} \) = \( \frac{50 ft⋅lb}{30 lbs.} \) = 1.67 ft.