ASVAB Mechanical Comprehension Practice Test 546351 Results

	Your Results	Global Average
Questions	5	5
Correct	0	3.59
Score	0%	72%

Review

1 If you lift a 28 lbs. rock 43 ft. from the ground, how much work have you done?

70% Answer Correctly

	1204 ft⋅lb
	71 ft⋅lb
	0 ft⋅lb
	602 ft⋅lb

Solution

Work is force times distance. In this case, the force is the weight of the rock so:
\( W = F \times d \)
\( W = 28 \times 43 \)
\( W = 1204 \)

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

84% Answer Correctly

	wedge
	inclined plane
	first-class lever
	none of these

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.

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

70% Answer Correctly

	second-class lever
	third-class lever
	first-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.

4 If the green box weighs 25 lbs. and is 2 ft. from the fulcrum, how much force would need to be applied at the blue arrow to balance the lever if the arrow's distance from the fulcrum is 6 ft.?

62% Answer Correctly

	8.33 lbs.
	16.67 lbs.
	0 lbs.
	33.33 lbs.

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

R_b = \( \frac{R_ad_a}{d_b} \) = \( \frac{25 lbs. \times 2 ft.}{6 ft.} \) = \( \frac{50 ft⋅lb}{6 ft.} \) = 8.33 lbs.

5 If the green arrow in this diagram represents 720 ft⋅lb of work, how far will the box move if it weighs 240 pounds?

72% Answer Correctly

	480 ft.
	1 ft.
	3 ft.
	6 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 720 ft⋅lb and the resistance force is 240 lbs. and we need to calculate the resistance distance:

W_in = F_resistance x d_resistance
720 ft⋅lb = 240 lbs. x d_resistance
d_resistance = \( \frac{720ft⋅lb}{240 lbs.} \) = 3 ft.