ASVAB Mechanical Comprehension Practice Test 804107 Results

	Your Results	Global Average
Questions	5	5
Correct	0	3.40
Score	0%	68%

Review

1 The radius of the axle is 7, the radius of the wheel is 10, and the blue box weighs 65 lbs. What is the effort force necessary to balance the load?

53% Answer Correctly

	10 lbs.
	17 lbs.
	45.45 lbs.
	8.43 lbs.

Solution

The mechanical advantage of a wheel and axle is the input radius divided by the output radius:

MA = \( \frac{r_i}{r_o} \)

In this case, the input radius (where the effort force is being applied) is 10 and the output radius (where the resistance is being applied) is 7 for a mechanical advantage of \( \frac{10}{7} \) = 1.43

MA = \( \frac{load}{effort} \) so effort = \( \frac{load}{MA} \) = \( \frac{65 lbs.}{1.43} \) = 45.45 lbs.

The steering wheel of a car is an example of which type of simple machine?

89% Answer Correctly

	fixed pulley
	block and tackle
	first-class lever
	wheel and axle

Solution

A wheel and axle uses two different diameter wheels mounted to a connecting axle. Force is applied to the larger wheel and large movements of this wheel result in small movements in the smaller wheel. Because a larger movement distance is being translated to a smaller distance, force is increased with a mechanical advantage equal to the ratio of the diameters of the wheels. An example of a wheel and axle is the steering wheel of a car.

3 If the green box weighs 30 lbs. and is 9 ft. from the fulcrum, how far from the fulcrum would a 15 lbs. weight need to be placed to balance the lever?

61% Answer Correctly

	6 ft.
	36 ft.
	18 ft.
	0 ft.

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

d_b = \( \frac{R_ad_a}{R_b} \) = \( \frac{30 lbs. \times 9 ft.}{15 lbs.} \) = \( \frac{270 ft⋅lb}{15 lbs.} \) = 18 ft.

The mass of an object correlates to the size of the object but ultimately depends on:

66% Answer Correctly

	the object's weight
	gravity
	the object's potential energy
	the object's density

Solution

Mass is a measure of the amount of matter in an object. In general, larger objects have larger mass than smaller objects but mass ultimately depends on how compact (dense) a substance is.

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

70% Answer Correctly

	inclined plane
	first-class lever
	second-class lever
	third-class lever

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.