ASVAB Mechanical Comprehension Practice Test 478472 Results

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

Review

1 If this lever is in equilibrium with an effort force of 5.0 ft. lb. at the blue arrow and a resistance force of 4 ft. lb. at the green box, what is its mechanical advantage?

48% Answer Correctly

	0.8
	3.8
	2.4
	2.8

Solution

Mechanical advantage (MA) is the ratio by which effort force relates to resistance force. If both forces are known, calculating MA is simply a matter of dividing resistance force by effort force:

MA = \( \frac{F_r}{F_e} \) = \( \frac{4 ft.}{5.0 ft.} \) = 0.8

In this case, the mechanical advantage is less than one meaning that each unit of effort force results in just 0.8 units of resistance force. However, a third class lever like this isn't designed to multiply force like a first class lever. A third class lever is designed to multiply distance and speed at the resistance by sacrificing force at the resistance. Different lever styles have different purposes and multiply forces in different ways.

Depending on where you apply effort and resistance, the wheel and axle can multiply:

45% Answer Correctly

	force or speed
	force or distance
	power or distance
	speed or power

Solution

If you apply the resistance to the axle and the effort to the wheel, the wheel and axle will multiply force and if you apply the resistance to the wheel and the effort to the axle, it will multiply speed.

Which of the following is not a type of simple machine?

58% Answer Correctly

	pulley
	screw
	lever
	gear

Solution

The six types of simple machines are the lever, wheel and axle, pulley, inclined plane, wedge, and screw.

4 A = 9 ft., the green box weighs 25 lbs., and the blue box weighs 75 lbs. What does distance B need to be for this lever to balance?

65% Answer Correctly

	1 ft.
	3 ft.
	9 ft.
	225 ft.

Solution

In order for this lever to balance, the torque acting on side A must equal the torque acting on side B. Torque is weight x distance from the fulcrum which means that the following must be true for the lever to balance:

f_Ad_A = f_Bd_B

For this problem, the equation becomes:

25 lbs. x 9 ft. = 75 lbs. x d_B

d_B = \( \frac{25 \times 9 ft⋅lb}{75 lbs.} \) = \( \frac{225 ft⋅lb}{75 lbs.} \) = 3 ft.

A box is resting on a smooth floor. Static friction is present:

59% Answer Correctly

	at all times
	only if normal force is present
	when an attempt is made to move the box
	if the coefficient of friction is greater than one

Solution

For any given surface, the coefficient of static friction is higher than the coefficient of kinetic friction. More force is required to initally get an object moving than is required to keep it moving. Additionally, static friction only arises in response to an attempt to move an object (overcome the normal force between it and the surface).