(4)+Work,+Energy,+and+Power

PAGE EDITOR(S): Fabi Praca, Alex Haubold, Dorothy Kafka, Dan Trauner, Tom Crockett


 * Due Date: 11/23/09 (Monday)**

**Natland Note (11/30/09):** Animations look good, but the word document is a bit rough at points (hard to follow/read). You probably want to move that to the top of the page. Additionally, more people need to post to the webpage. Also, looking at the directions on the homepage, you want to have more links posted.

There is a really cool interactive simulation similar to this roller coaster image that can be used to explain energy conservation (or situations including friction) at [].


 * The following link is to our notes


 * The car on the left undergoes the greatest displacement, but the smallest force. This is because the positive vertical component of the normal force is the greatest. In comparison, the car on the right undergoes the smallest displacement, but the greatest force; the positive vertical component of the normal force is the smallest.

  
 * When no work is done, the total mechanical energy remains constant though the potential and kinetic energies may change. However, when negative work is done (by the net force, in this case friction), the total mechanical energy decreases.
 * The total mechanical energy remains constant, but the spring potential energy, gravitational potential energy, and kinetic energy change. All three types of energy always add up to the total mechanical energy.

This animation shows the relationship between the initial velocity of a car and its skidding distance. The greater the initial velocity, the greater the skidding distance. Also, when there is a greater skidding distance, there is more negative work done to the car by friction.



This is a demonstration from the MIT Physics department showing gravitational potential and kinetic energy --> []

This is a really good site where you can find conceptual explanations for various automobile-related problems --> []

These are some practice work problems. []

http://www.ac.wwu.edu/~vawter/PhysicsNet/Topics/Work/WorkEngergyTheorem.html (This site explains the Work Energy Theorem really well.)

http://galileoandeinstein.physics.virginia.edu/lectures/momentum.html (This site helps explain work and energy in comparison to momentum.)

http://www.school-for-champions.com/science/work_energy.htm ( This site layouts out all of the equations to know regarding work and energy)

As Mr. Natland mentioned in class one of the first few days we learned about energy, work, and power: even though a chocolate chip cookie has more latent energy than an equal amount of TNT, the TNT is more dangerous because it is high-power (can release its energy MUCH more quickly). Here is a table with relative energies:  
 * Object || Calories || Joules || Compared to TNT ||
 * bullet (moving at speed of sound, 1000 ft per second) || 0.01 || 40 J || 0.015 ||
 * battery (flashlight) || 0.01 || 40 J || 0.015 ||
 * battery (computer) || 0.1 || 400 J || 0.15 ||
 * TNT (trinitrotoluene) || 0.651 || 2723 J || 1 ||
 * modern High Explosive (PETN) || 1 ||  || 1.6 ||
 * chocolate chip cookies || 5 || 21 kJ || 8 ||
 * butter || 7 || 29 kJ || 11 ||
 * gasoline || 10 || 42 kJ || 15 ||
 * methane gas (CH4) || 13 || 54 kJ || 20 ||
 * hydrogen gas (H2) for fuel cell || 26 || 110 kJ || 40 ||
 * asteroid or meteor (30 km/sec) || 107 || 450 kJ || 165 ||
 * uranium-235 || 20 million Cal || 84 billion J || 30 million ||

You may find a few interesting figures in this table. According to the site, "For the same weight of fuel, nuclear reactions release about 1 million times more energy than do chemical or food reactions." No wonder we bother using nuclear reactors for power at all! Unfortunately Uranium-235 only makes up about 0.7% of the naturally occurring Uranium. At 30 million times the energy of TNT though, not much is needed at once.

SOME MORE PROBLEMS 1. A block of ice slides down a frictionless ramp at angle q = 50° while an ice worker pulls on the block (via a rope) with a force that has a magnitude of 50 N and is directed up the ramp. As the block slides through distance d = 0.50 m along the ramp, its kinetic energy increases by 80 J. How much greater would its kinetic energy have been if the rope had not been attached to the block?

2. The problem statement, all variables and given/known data At time ti, the kinetic energy of a particle is 35.5 J and its potential energy is 8.16 J.At some later time tf, its kinetic energy is 9.38 J. If only conservative forces act on the parti- cle, what is its potential energy tf ? Answer in units of J. If the potential energy at time tf is 6.95 J, what is the work done by the nonconservative forces acting on the particle? Answer in units of J.

3. 1. The problem statement, all variables and given/known data A motorcycle (mass of cycle plus rider = 250 kg) is traveling at a steady speed of 20 m/s. The force of air resistance acting on the cycle and rider is 200 N. Find the power necessary to sustain this speed if (a) the road is level and (b) the road is sloped upward ar 37degrees with respect to the horizontal.

(the six animations showing energy transformation and work applied over time)
 * __SOURCES__**[[image:file:///Users/olivia/Desktop/nw0315-n.gif]]
 * __[]__**

(interactive roller coaster Java applet)
 * __[]__**

[] MIT Potential/Kinetic Energy Demonstration

[] Automobile-related conceptual momentum problems

[] Information regarding relative energy/power (chocolate chip cookie and TNT etc)

http://www.physicsforums.com/showthread.php?t=328024 ( Extra Problems)

[] (Helpful for Elevator related Energy Problems. Just click on the link and follow the instructions.)

http://www.physicsclassroom.com/mmedia/energy/hh.cfm (For sled animation)

http://www.physicsclassroom.com/mmedia/energy/cs.cfm (For skid animation)