ASVAB Mechanical Comprehension Practice Test 313681 Results

	Your Results	Global Average
Questions	5	5
Correct	0	2.94
Score	0%	59%

Review

1 If the green box weighs 30 lbs. and is 7 ft. from the fulcrum, how far from the fulcrum would a 5 lbs. weight need to be placed to balance the lever?

61% Answer Correctly

	14 ft.
	42 ft.
	4 ft.
	168 ft.

Solution

To balance this lever the torques on each side of the fulcrum 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 left side of the fulcrum and b the right, R is resistance (weight) and d is the distance from the fulcrum.

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

d_b = \( \frac{R_ad_a}{R_b} \) = \( \frac{30 lbs. \times 7 ft.}{5 lbs.} \) = \( \frac{210 ft⋅lb}{5 lbs.} \) = 42 ft.

2 If the green box weighs 60 lbs. and 60 lbs. of force is applied 9 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

	6 ft.
	4.5 ft.
	9 ft.
	3 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 = \( \frac{R_bd_b}{R_a} \) = \( \frac{60 lbs. \times 9 ft.}{60 lbs.} \) = \( \frac{540 ft⋅lb}{60 lbs.} \) = 9 ft.

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

79% Answer Correctly

	1
	4
	2
	0

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.

The advantage of using a third-class lever is that it increases:

37% Answer Correctly

	the force applied to the load
	the speed of the load
	the distance traveled by the load
	the mechanical advantage of the lever

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.

Coplanar forces:

62% Answer Correctly

	have opposite dimensions
	act in a common plane
	act along the same line of action
	pass through a common point

Solution

Collinear forces act along the same line of action, concurrent forces pass through a common point and coplanar forces act in a common plane.