ASVAB Mechanical Comprehension Practice Test 966244 Results

	Your Results	Global Average
Questions	5	5
Correct	0	3.23
Score	0%	65%

Review

1 If input effort is 100 ft⋅lb, what output effort will be produced by a machine with a mechanical advantage of 9?

79% Answer Correctly

	0ft⋅lb
	1800ft⋅lb
	3600ft⋅lb
	900 ft⋅lb

Solution

Mechanical advantage is the ratio of output force to input force and tells us by how many times a machine multiplies input effort. So, a machine with a mechanical advantage of 9 will multiply an input effort of 100 ft⋅lb by 9 to produce an output effort of 900 ft⋅lb.

2 If the green box weighs 75 lbs. and is 9 ft. from the fulcrum, how much weight would need to be placed at the blue arrow to balance the lever if the arrow's distance from the fulcrum is 8 ft.?

63% Answer Correctly

	42.19 lbs.
	84.38 lbs.
	337.5 lbs.
	9 lbs.

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 R_b, our missing value, and plugging in our variables yields:

R_b = \( \frac{R_ad_a}{d_b} \) = \( \frac{75 lbs. \times 9 ft.}{8 ft.} \) = \( \frac{675 ft⋅lb}{8 ft.} \) = 84.38 lbs.

If the handles of a wheelbarrow are 3 ft. from the wheel axle, what force must you exert to lift the handles if it's carrying a 270 lb. load concentrated at a point 0.5 ft. from the axle?

56% Answer Correctly

	0.83 lbs
	45 lbs
	810 lbs
	90 lbs

Solution

This problem describes a second-class lever and, for a second class lever, the effort force multiplied by the effort distance equals the resistance force multipied by the resistance distance: F_ed_e = F_rd_r. Plugging in the variables from this problem yields:

F_e x 3 ft. = 270 lbs x 0.5 ft
F_e = 135 ft-lb. / 3 ft
F_e= 45 lbs

A wedge is most similar to what other type of simple machine?

70% Answer Correctly

	first-class lever
	third-class lever
	second-class lever
	inclined plane

Solution

The wedge is a moving inclined plane that is used to lift, hold, or break apart an object. A wedge converts force applied to its blunt end into force perpendicular to its inclined surface. In contrast to a stationary plane where force is applied to the object being moved, with a wedge the object is stationary and the force is being applied to the plane. Examples of a wedge include knives and chisels.

Concurrent forces:

55% Answer Correctly

	act in a common dimension
	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.