## ASVAB Mechanical Comprehension Practice Test 740104

 Questions 5 Topics Efficiency, Force Lines of Action, Mass, Normal Force vs. Weight, Power

#### Study Guide

###### Efficiency

The efficiency of a machine describes how much of the power put into the machine is turned into movement or force. A 100% efficient machine would turn all of the input power into output movement or force. However, no machine is 100% efficient due to friction, heat, wear and other imperfections that consume input power without delivering any output.

###### Force Lines of Action

Collinear forces act along the same line of action, concurrent forces pass through a common point and coplanar forces act in a common plane.

###### Mass

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.

###### Normal Force vs. Weight

Normal force arises on a flat horizontal surface in response to an object's weight pressing it down. Consequently, normal force is generally equal to the object's weight.

###### Power

Power is the rate at which work is done, P = w/t, or work per unit time. The watt (W) is the unit for power and is equal to 1 joule (or newton-meter) per second. Horsepower (hp) is another familiar unit of power used primarily for rating internal combustion engines. A 1 hp machine does 550 ft⋅lb of work in 1 second and 1 hp equals 746 watts.