ASVAB Mechanical Comprehension Practice Test 419630 Results

	Your Results	Global Average
Questions	5	5
Correct	0	3.31
Score	0%	66%

Review

1 40 lbs. of effort is used by a machine to lift a 120 lbs. box. What is the mechanical advantage of the machine?

84% Answer Correctly

	9
	5
	3
	2.7

Solution

Mechanical advantage is resistance force divided by effort force:

MA = \( \frac{F_r}{F_e} \) = \( \frac{120 lbs.}{40 lbs.} \) = 3

2 If the force applied at the blue arrow over 8 ft. moves the green box 2.67 ft., what is the mechanical advantage of this lever?

55% Answer Correctly

	3
	3.3
	9
	4.5

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 = \( \frac{8 ft.}{2.67 ft.} \) = 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.

A block and tackle with four pulleys would have a mechanical advantage of:

79% Answer Correctly

	0
	1
	4
	2

Solution

Two or more pulleys used together constitute a block and tackle which, unlike a fixed pulley, does impart mechanical advantage as a function of the number of pulleys that make up the arrangement. So, for example, a block and tackle with three pulleys would have a mechanical advantage of three.

4 If the green box weighs 60 lbs. and 65 lbs. of force is applied 3 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

	1.08 ft.
	1.63 ft.
	6.5 ft.
	3.25 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 = \( \frac{R_bd_b}{R_a} \) = \( \frac{65 lbs. \times 3 ft.}{60 lbs.} \) = \( \frac{195 ft⋅lb}{60 lbs.} \) = 3.25 ft.

A shovel is an example of which class of lever?

56% Answer Correctly

	third
	a shovel is not a lever
	second
	first

Solution

A third-class lever is used to increase distance traveled by an object in the same direction as the force applied. The fulcrum is at one end of the lever, the object at the other, and the force is applied between them. This lever does not impart a mechanical advantage as the effort force must be greater than the load but does impart extra speed to the load. Examples of third-class levers are shovels and tweezers.