ASVAB Mechanical Comprehension Practice Test 77012 Results

	Your Results	Global Average
Questions	5	5
Correct	0	2.84
Score	0%	57%

Review

1 If input effort is 900 ft⋅lb, what output effort will be produced by a machine with a mechanical advantage of 8?

79% Answer Correctly

	3600ft⋅lb
	14400ft⋅lb
	7200 ft⋅lb
	28800ft⋅lb

Solution

Mechanical advantage is the ratio of output force to input force and tells us by how many times a machine multiplies input effort. So, a machine with a mechanical advantage of 8 will multiply an input effort of 900 ft⋅lb by 8 to produce an output effort of 7200 ft⋅lb.

2 If the green box weighs 15 lbs. and is 9 ft. from the fulcrum, how far from the fulcrum would a 20 lbs. force need to be applied to balance the lever?

58% Answer Correctly

	6.75 ft.
	135 ft.
	27 ft.
	13.5 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_b, our missing value, and plugging in our variables yields:

d_b = \( \frac{R_ad_a}{R_b} \) = \( \frac{15 lbs. \times 9 ft.}{20 lbs.} \) = \( \frac{135 ft⋅lb}{20 lbs.} \) = 6.75 ft.

The science that deals with motion and the forces that produce motion is called which of the following?

57% Answer Correctly

	mechanics
	aeronautics
	physics
	engineering

Solution

Mechanics deals with motion and the forces that produce motion.

The mechanical advantage of a third class lever is always:

37% Answer Correctly

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

For any given surface, the coefficient of static friction is ___________ the coefficient of kinetic friction.

54% Answer Correctly

	opposite
	higher than
	equal to
	lower than

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).