ASVAB Mechanical Comprehension Practice Test 440059 Results

	Your Results	Global Average
Questions	5	5
Correct	0	2.64
Score	0%	53%

Review

1 If the green arrow in this diagram represents 220 ft⋅lb of work, how far will the box move if it weighs 110 pounds?

73% Answer Correctly

	220 ft.
	2 ft.
	1 ft.
	55 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 220 ft⋅lb and the resistance force is 110 lbs. and we need to calculate the resistance distance:

W_in = F_resistance x d_resistance
220 ft⋅lb = 110 lbs. x d_resistance
d_resistance = \( \frac{220ft⋅lb}{110 lbs.} \) = 2 ft.

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

54% Answer Correctly

	opposite
	equal to
	higher than
	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).

3 If a 35 lbs. weight is placed 1 ft. from the fulcrum at the blue arrow and the green box is 8 ft. from the fulcrum, how much would the green box have to weigh to balance the lever?

61% Answer Correctly

	4.38 lbs.
	1.46 lbs.
	13.13 lbs.
	8.75 lbs.

Solution

To balance this lever the torques on each side of the fulcrum 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 left side of the fulcrum and b the right, R is resistance (weight) and d is the distance from the fulcrum.

Solving for R_a, our missing value, and plugging in our variables yields:

R_a = \( \frac{R_bd_b}{d_a} \) = \( \frac{35 lbs. \times 1 ft.}{8 ft.} \) = \( \frac{35 ft⋅lb}{8 ft.} \) = 4.38 lbs.

Force of friction due to kinetic friction is __________ the force of friction due to static friction.

40% Answer Correctly

	lower than
	higher than
	the same as
	opposite

Solution

The formula for force of friction (F_f) is the same whether kinetic or static friction applies: F_{f =}μF_N. To distinguish between kinetic and static friction, μ_k and μ_s are often used in place of μ.

The mechanical advantage of a third class lever is always:

37% Answer Correctly

	equal to one
	less than one
	not equal to 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.