ASVAB Mechanical Comprehension Practice Test 912366 Results

	Your Results	Global Average
Questions	5	5
Correct	0	2.76
Score	0%	55%

Review

The mechanical advantage of a third class lever is always:

37% Answer Correctly

	less than one
	equal to one
	not equal to one
	greater than one

Solution

A third class lever is designed to multiply distance and speed at the expense of effort force. Because the effort force is greater than the resistance, the mechanical advantage of a third class lever is always less than one.

An example of a third class lever is a broom. The fulcrum is at your hand on the end of the broom, the effort force is your other hand in the middle, and the resistance is at the bottom bristles. The effort force of your hand in the middle multiplies the distance and speed of the bristles at the bottom but at the expense of producing a brushing force that's less than the force you're applying with your hand.

Assuming force applied remains constant, which of the following will result in more work being done?

53% Answer Correctly

	increasing the coefficient of friction
	moving the object with more acceleration
	moving the object farther
	moving the object with more speed

Solution

Work is accomplished when force is applied to an object: W = Fd where F is force in newtons (N) and d is distance in meters (m). Thus, the more force that must be applied to move an object, the more work is done and the farther an object is moved by exerting force, the more work is done.

3 What is the efficiency of a machine has work input of 240 ft⋅lb and work output of 228 ft⋅lb?

67% Answer Correctly

	1%
	0%
	95%
	190%

Solution

Due to friction, a machine will never be able to utilize 100% of its work input. A certain percentage of that input will be lost in overcoming friction within the machine. Effeciency is a measure of how much of a machine's work input can be turned into useful work output and is calculated by dividing work output by work input and multiplying the result by 100:
\( Efficiency = \frac{Work_{out}}{Work_{in}} \times 100 \) \( = \frac{228 ft⋅lb}{240 ft⋅lb} \times 100 \) \( = 95% \) %

Which of the following statements about this pulley configuration is false?

48% Answer Correctly

	This is a block and tackle pulley configuration
	Changes the direction of and multiplies the effort force
	Only multiplies the effort force
	Mechanical advantage is the number of ropes that support the resistance

Solution

A block and tackle is a combination of one or more fixed pulleys and one or more movable pulleys where the fixed pulleys change the direction of the effort force and the movable pulleys multiply it. The mechanical advantage is equal to the number of times the effort force changes direction and can be increased by adding more pulley wheels to the system. An easy way to find the mechanical advantage of a block and tackle pulley system is to count the number of ropes that support the resistance.

Collinear forces:

72% Answer Correctly

	are unrelated to each other
	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.