ASVAB Mechanical Comprehension Practice Test 493973 Results

	Your Results	Global Average
Questions	5	5
Correct	0	3.23
Score	0%	65%

Review

1 If the green arrow in this diagram represents 420 ft⋅lb of work, how far will the box move if it weighs 210 pounds?

73% Answer Correctly

	105 ft.
	840 ft.
	420 ft.
	2 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 420 ft⋅lb and the resistance force is 210 lbs. and we need to calculate the resistance distance:

W_in = F_resistance x d_resistance
420 ft⋅lb = 210 lbs. x d_resistance
d_resistance = \( \frac{420ft⋅lb}{210 lbs.} \) = 2 ft.

The principle of conservation of mechanical energy states that, as long as no other forces are applied, what will remain constant as an object falls?

45% Answer Correctly

	potential energy
	acceleration
	kinetic energy
	total mechanical energy

Solution

As an object falls, its potential energy is converted into kinetic energy. The principle of conservation of mechanical energy states that, as long as no other forces are applied, total mechanical energy (PE + KE) of the object will remain constant at all points in its descent.

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

89% Answer Correctly

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

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.

4 If the green box weighs 25 lbs. and is 2 ft. from the fulcrum, how much force would need to be applied at the blue arrow to balance the lever if the arrow's distance from the fulcrum is 6 ft.?

62% Answer Correctly

	16.67 lbs.
	8.33 lbs.
	2.08 lbs.
	4.17 lbs.

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

R_b = \( \frac{R_ad_a}{d_b} \) = \( \frac{25 lbs. \times 2 ft.}{6 ft.} \) = \( \frac{50 ft⋅lb}{6 ft.} \) = 8.33 lbs.

Torque involves a perpendicular force applied to a lever arm that moves around a center of rotation. Increasing the length of the lever arm will do which of the following?

55% Answer Correctly

	decrease applied force
	decrease torque
	increase applied force
	increase torque

Solution

Torque measures force applied during rotation: τ = rF. Torque (τ, the Greek letter tau) = the radius of the lever arm (r) multiplied by the force (F) applied. Radius is measured from the center of rotation or fulcrum to the point at which the perpendicular force is being applied. The resulting unit for torque is newton-meter (N-m) or foot-pound (ft-lb).