ASVAB Mechanical Comprehension Practice Test 370300 Results

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

Review

Friction resists movement in a direction __________ to the movement.

81% Answer Correctly

	normal
	parallel
	opposite
	perpendicular

Solution

Friction resists movement. Kinetic (also called sliding or dynamic) friction resists movement in a direction opposite to the movement. Because it opposes movement, kinetic friction will eventually bring an object to a stop. An example is a rock that's sliding across ice.

2 What is the efficiency of a machine has work input of 165 ft⋅lb and work output of 49 ft⋅lb?

67% Answer Correctly

	0%
	120%
	30%
	15%

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:
\( Efficiency = \frac{Work_{out}}{Work_{in}} \times 100 \) \( = \frac{49 ft⋅lb}{165 ft⋅lb} \times 100 \) \( = 30% \) %

The mechanical advantage of a third class lever is always:

37% Answer Correctly

	not equal to one
	equal to one
	less than 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.

4 If the handles of a wheelbarrow are 2.5 ft. from the wheel axle and the load is concentrated at a point 1.0 ft. from the axle, how many pounds of load will a 120 lbs. force lift?

47% Answer Correctly

	0
	382.8
	300
	-29.3

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. In this problem we're looking for resistance force:
\( F_r = \frac{F_e d_e}{d_r} \)
\( F_r = \frac{120 \times 2.5}{1.0} \)
\( F_r = \frac{300.0}{1.0} \)
\( F_r = 300 \)

An inclined plane increases ___________ to reduce ____________.

58% Answer Correctly

	force, distance
	force, power
	distance, force
	distance, power

Solution

An inclined plane is a simple machine that reduces the force needed to raise an object to a certain height. Work equals force x distance and, by increasing the distance that the object travels, an inclined plane reduces the force necessary to raise it to a particular height. In this case, the mechanical advantage is to make the task easier. An example of an inclined plane is a ramp.