ReadingGuide2051/ReadingGuide_Ch7_Solution.html at master · jtaou/ReadingGuide2051 · GitHub

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<h1>Chapter 7 &ndash; Work and Kinetic Energy</h1>

<h3>Introduction</h3>

<p>- Instead of using forces to solve problems it is often more convienent to
use energy arguments.</p>

<p>- When a sprinter runs, she does ________ on herself, which adds to her
kinetic energy. <span id="ans">Work</span></p>

<h3>7.1 &ndash; Work</h3>

<p><span id="comm">- Add the vector dot product questions from chapter 2
here.</span></p>

<p><span id="prob">- From the Errata: In Volume 1, Chapter 7 (pg. 336), the
Openstax textbook states &ldquo;In physics, work represents a type of
energy.&rdquo; Work is not a type of energy; work is the transfer of energy by
an applied force over some displacement. Objects and systems have energy, but
they do not have work. Objects and systems do work by applying a force over
some distance on another object or system.</span></p>

<p>- What is work? <span id="ans">Equation 7.1.</span></p>

<p>- What is work done by a force? <span id="ans">The integral of the force
with respect to the displacement along the displacement. Equation
7.2.</span></p>

<p>- What is the SI unit for work? What other base units is it equivalent to?
<span id="ans">Joule (J). 1J = 1N*m.</span></p>

<p>- In figure 7.3, what is the work done on the lawnmower? What is the work
done on the briefcase in (b) and (c)? Why? <span id="ans">Lawnmower &ndash;
F*d*cos(theta). (b) 0. The displacement is 0. (c) 0. The angle between the
force and displacement is 90 degrees.</span></p>

<p>- What is the work done by friction?<span id="ans">Equation 7.3.</span></p>

<p>- How is the work done by related to the work done against? <span
id="comm">NOTE: Sometimes work done against an object is called work done on an
object</span> <span id="ans">They are equal but opposite directions.</span></p>

<p>- What is the work done by gravity? <span id="ans">Equation 7.4.</span></p>

<p>- In Example 7.3 (Shelving a Book), why is the answer to (b) zero? <span
id="ans">There angle between the force and displacement is 90 degrees.
</span></p>

<p>- The equation at the top of pdf page 324 shows work in vector component
form. Look at example 7.4 (Work Done by a Variable Force over a Curved Path) to
understand how to apply it.</p>

<p>- What is the work done by a spring? <span id="ans">Equation 7.5.</span></p>

<p>- Figures 7.8 and 7.9 show that work is the integral of force as a function
of displacement. 7.8 is an arbitrary force and 7.9 is the spring force.</p>

<p>- In the problem statement of Example 7.5 (Work Done by a Spring Force), is
work required the work done against or by the spring? <span
id="ans">against</span></p>

<h3>7.2 &ndash; Kinetic Energy</h3>

<p>- What is kinetic energy? <span id="ans">Equation 7.6.</span></p>

<p>- What are the units of kinetic energy? <span id="ans">Joules.</span></p>

<p>- Example 7.7 shows that the kinetic energy of an object depends on the
reference frame.</p>

<p>- What are the five types of kinetic energy described in the book? What type
of motion do they represent? <span id="ans">Translational KE &ndash;
translational motion. Rotational KE &ndash; rotating motion. Vibrational KE
&ndash; vibrational motion. Internal KE &ndash; internal motion. Thermal KE
&ndash; random motion.</span></p>

<h3>7.3 &ndash; Work-Energy Theorem</h3>

<p>- What is the work-energy theorem? <span id="ans">Equation 7.9</span></p>

<p>- What is the problem solving strategy for problems involving the
work-energy theorem? <span id="ans">Draw a free-body diagram for each force on
the object. Determine whether or not each force does work over the displacement
in the diagram. Be sure to keep any positive or negative signs in the work
done. Add up the total amount of work done by each force. Set this total work
equal to the change in kinetic energy and solve for any unknown parameter.
Check your answers.</span></p>

<p>- In example 7.10 (Determining a Stopping Force), what is the stopping force
of the bullet? Notice that you could also use kinematics to solve this problem.
<span id="ans">960N.</span></p>

<h3>7.4 &ndash; Power</h3>

<p>- What is power? <span id="ans">Equation 7.11</span></p>

<p>- What is the unit of power? <span id="ans">Watt. 1 J/s = 1W.</span></p>

<p>- What is horespower? <span id="ans">1hp = 746W.</span></p>

<p>- What is the equation for power in terms of velocity? <span
id="ans">Equation 7.12.</span></p>

<p></p>
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