ASVAB Mechanical Comprehension Practice Test 934436 Results

	Your Results	Global Average
Questions	5	5
Correct	0	3.56
Score	0%	71%

Review

1 If a 40 lbs. weight is placed 1 ft. from the fulcrum at the blue arrow and the green box is 2 ft. from the fulcrum, how much would the green box have to weigh to balance the lever?

61% Answer Correctly

	5 lbs.
	20 lbs.
	40 lbs.
	60 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 = \( \frac{R_bd_b}{d_a} \) = \( \frac{40 lbs. \times 1 ft.}{2 ft.} \) = \( \frac{40 ft⋅lb}{2 ft.} \) = 20 lbs.

2 If the force applied at the blue arrow over 4 ft. moves the green box 1.0 ft., what is the mechanical advantage of this lever?

56% Answer Correctly

	1
	4
	-3
	3.6

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 = \( \frac{4 ft.}{1.0 ft.} \) = 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.

Which of these is the formula for force?

77% Answer Correctly

	F = ma
	F = am²
	F = a/m
	F = m/a

Solution

Newton's Second Law of Motion states that "The acceleration of an object as produced by a net force is directly proportional to the magnitude of the net force, in the same direction as the net force, and inversely proportional to the mass of the object." This Law describes the linear relationship between mass and acceleration when it comes to force and leads to the formula F = ma or force equals mass multiplied by rate of acceleration.

When all forces acting on a system cancel each other out, this is called:

80% Answer Correctly

	equilibrium
	potential energy
	stasis
	rest

Solution

When a system is stable or balanced (equilibrium) all forces acting on the system cancel each other out. In the case of torque, equilibrium means that the sum of the anticlockwise moments about a center of rotation equal the sum of the clockwise moments.

Which of the following surfaces would have the highest coefficient of friction?

77% Answer Correctly

	steel
	marble
	ice
	concrete

Solution

Coefficient of friction (μ) represents how much two materials resist sliding across each other. Smooth surfaces like ice have low coefficients of friction while rough surfaces like concrete have high μ.