ASVAB Mechanical Comprehension Practice Test 334929 Results

	Your Results	Global Average
Questions	5	5
Correct	0	3.55
Score	0%	71%

Review

A ramp is an example of which kind of simple machine?

84% Answer Correctly

	wedge
	none of these
	first-class lever
	inclined plane

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.

An object's resistance to changes in direction is known as:

81% Answer Correctly

	inertia
	weight
	kinetic energy
	mass

Solution

The more mass a substance has the more force is required to move it or to change its direction. This resistance to changes in direction is known as inertia.

3 If the force applied at the blue arrow over 6 ft. moves the green box 1.5 ft., what is the mechanical advantage of this lever?

55% Answer Correctly

	3.6
	-5
	4
	1

Solution

Mechanical advantage (MA) can be calculated knowing only the distance the effort (blue arrow) moves and the distance the resistance (green box) moves. The equation is:

MA = \( \frac{E_d}{R_d} \)

where E_d is the effort distance and R_d is the resistance distance. For this problem, the equation becomes:

MA = \( \frac{6 ft.}{1.5 ft.} \) = 4

You might be wondering how having an effort distance of 4 times the resistance distance is an advantage. Remember the principle of moments. For a lever in equilibrium the effort torque equals the resistance torque. Because torque is force x distance, if the effort distance is 4 times the resistance distance, the effort force must be \( \frac{1}{4} \) the resistance force. You're trading moving 4 times the distance for only having to use \( \frac{1}{4} \) the force.

4 If the green arrow in this diagram represents 300 ft⋅lb of work, how far will the box move if it weighs 100 pounds?

72% Answer Correctly

	3 ft.
	33 ft.
	50 ft.
	0 ft.

Solution

The Law of Work states that the work put into a machine is equal to the work received from the machine under ideal conditions. In equation form, that's:

W_in = W_out
F_effort x d_effort = F_resistance x d_resistance

In this problem, the effort work is 300 ft⋅lb and the resistance force is 100 lbs. and we need to calculate the resistance distance:

W_in = F_resistance x d_resistance
300 ft⋅lb = 100 lbs. x d_resistance
d_resistance = \( \frac{300ft⋅lb}{100 lbs.} \) = 3 ft.

5 If the green box weighs 20 lbs. and 45 lbs. of force is applied 7 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

	5.25 ft.
	140 ft.
	15.75 ft.
	2 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 = \( \frac{R_bd_b}{R_a} \) = \( \frac{45 lbs. \times 7 ft.}{20 lbs.} \) = \( \frac{315 ft⋅lb}{20 lbs.} \) = 15.75 ft.