ASVAB Mechanical Comprehension Practice Test 429243 Results

	Your Results	Global Average
Questions	5	5
Correct	0	2.80
Score	0%	56%

Review

Coplanar forces:

61% Answer Correctly

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

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.

Which of the following is not true of a first-class lever?

51% Answer Correctly

	increases force
	changes the direction of force
	decreases distance
	increases distance

Solution

A first-class lever is used to increase force or distance while changing the direction of the force. The lever pivots on a fulcrum and, when a force is applied to the lever at one side of the fulcrum, the other end moves in the opposite direction. The position of the fulcrum also defines the mechanical advantage of the lever. If the fulcrum is closer to the force being applied, the load can be moved a greater distance at the expense of requiring a greater input force. If the fulcrum is closer to the load, less force is required but the force must be applied over a longer distance. An example of a first-class lever is a seesaw / teeter-totter.

Concurrent forces:

55% Answer Correctly

	pass through a common point
	act in a common plane
	act in a common dimension
	act along the same line of action

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.

4 A 370 lb. barrel is rolled up a 16 ft. ramp to a platform that's 5 ft. tall. What effort is required to move the barrel?

53% Answer Correctly

	231.3 lbs.
	173.4 lbs.
	115.6 lbs.
	38.5 lbs.

Solution

This problem describes an inclined plane and, for an inclined plane, 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 16 ft. = 370 lbs. x 5 ft.
F_e = \( \frac{1850 ft⋅lb}{16 ft.} \) = 115.6 lbs.

5 If the green box weighs 75 lbs. and is 7 ft. from the fulcrum, how far from the fulcrum would a 50 lbs. weight need to be placed to balance the lever?

61% Answer Correctly

	21 ft.
	3.5 ft.
	525 ft.
	10.5 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 = \( \frac{R_ad_a}{R_b} \) = \( \frac{75 lbs. \times 7 ft.}{50 lbs.} \) = \( \frac{525 ft⋅lb}{50 lbs.} \) = 10.5 ft.