Show pageOld revisionsBacklinksBack to top This page is read only. You can view the source, but not change it. Ask your administrator if you think this is wrong. ==== Kick Off Questions ==== The energy principle for a system states the change in energy of the system can be found in terms of work done and heat: $$\Delta E_{sys} = W_{surr} + Q$$ - What do $W_{surr}$ and $Q$ mean as they relate to the system? - The heat can be positive, negative or zero. What do each of these mean in terms of the direction of its flow? - The work done by a force is related to the force and the displacement. It can be calculated via the scalar or dot product. What are the conditions for the force and displacement that can result in positive work? Negative work? Zero work? ==== Project 7: Energy and Avengers==== Today, we are transitioning into talking about energy and are going to start small and examine energy from a few different scenarios. These scenarios highlight the idea of choosing systems and will ask you to analyze each problem from two different systems. This will hopefully help you all compare and contrast these two different approaches to solving energy problems. <WRAP info> ==== Project 7: Learning Concepts ==== * Relationship Between Force and Energy - Work * Choosing a system * Conservation of Energy * Potential and Kinetic Energy </WRAP> ===== Scenario 7a: Iron Man speeds up a train ===== Iron Man encounters a train (mass = $1.35 \times 10^6$ kg) that has run out of fuel 1000 m before the train station. He decides to put on his blasters (which have a force of 20 MN), and he pushes the train for 500 m to get it up to speed. He's hoping that friction for the rest of the way will slow down the train by the time it arrives at the station. Assuming the train's wheels are locked, Iron Man is able to overcome static friction and the coefficient of kinetic friction for steel on steel is $\mu_k = 0.74$. Choice 1: System = train + Iron Man + Earth Choice 2: System = train 1. For each choice of system above, answer the following questions: * Is energy conserved in the system? Why/why not? * Is work done on the system? Is it positive or negative? How do you know? * Draw the energy bar charts for the scenario. * Draw an energy vs time graph showing all mechanical energies, including the total system mechanical energy. 2. Pick a system to calculate how fast the train will going when it gets to the station. 3. Which system did you choose for your analysis? Why? ===== Scenario 7b: Hawkeye Launches Arrow ===== Hawkeye is standing the edge of a tall building (80 m) and needs to fire an arrow into the sky as a warning to the other avengers. He releases the arrow with an initial speed of 50 m/s at an angle of 60 degrees. Consider this situation from the instant after the arrow is launched. Choice 1: System = Arrow + Earth Choice 2: System = Arrow 1. For each choice of system above, answer the following questions: * Is energy conserved in the system? Why/why not? * Is work done on the system? Is it positive or negative? How do you know? * Draw the energy bar charts for the scenario. * Draw an energy vs time graph showing all mechanical energies, including the total system mechanical energy. 2. Pick a system to calculate the maximum height that the arrow will reach in the sky. 3. Which system did you choose for your analysis? Why? ===== Scenario 7c: Spiderman drops an apple ===== Spiderman is chilling on top of a skyscraper (120 m) eating his lunch, when he accidentally drops his apple. The apple then plummets toward an unsuspecting people on the street below. Choice 1: System = Apple Choice 2: System = Apple + Earth 1. For each choice of system above, answer the following questions: * Is energy conserved in the system? Why/why not? * Is work done on the system? Is it positive or negative? How do you know? * Draw the energy bar charts for the scenario. * Draw an energy vs time graph showing all mechanical energies, including the total system mechanical energy. 2. Spiderman decides to shoot a web to try to catch the apple before it hits a person on the street. Pick a system to calculate how much work Spiderman must do to stop the apple before it hits someone. 3. Which system did you choose for your analysis? Why? /* ===== Scenario 7d: Captain Marvel lowers the Infinity Gauntlet ===== In the midst of the battle with Thanos, Captain Marvel obtains the very precious infinity gauntlet (m = 2 kg). When she finds it, she raises the gauntlet above her head in victory but then realizes that may be a poor idea considering all the bad guys around. She then lowers the gauntlet again. Consider this time period, when Captain Marvel raises then lowers the infinity gauntlet. Choice 1: System = Infinity Gauntlet Choice 2: System = Infinity Gauntlet + Earth 1. For each choice of system above, answer the following questions: * Is energy conserved in the system? Why/why not? * Is work done on the system? Is it positive or negative? How do you know? * Draw the energy bar charts for the scenario. * Draw an energy vs time graph showing all mechanical energies, including the total system mechanical energy. 2. When Captain Marvel lowers the infinity gauntlet, how much work does she do? 3. Which system did you choose for your analysis? Why? ====== Project 7e: Hulk Trap ====== Black Widow unfortunately finds the Hulk trapped in a net by the ceiling at a height of 12 meters, which is tied to an anchor on the floor. Black Widow wants to rescue the Hulk but doesn't want him mad at her for just dropping him directly to the floor. If the Hulk weighs 566 kg, how much weight should the Black Widow attach to the other end of the rope so that the Hulk will land on the ground with a speed of 3 m/s? ====== Project 7f: The Black Widow ====== The Black Widow is caught in a trap and is sliding down an oil-slicked incline of angle 32 degrees. Ant-Man while engaging in combat with Kang the Conqueror throws a spring of k = 320 N/m that he enlarges as it is thrown and it lands at the bottom of the incline and becomes 8m long. The Black Widow needs to know how far away from the spring she is so she can figure how fast she needs to hit it in order to escape the incline of 25m length. Iron Man estimates that if she hits the spring from her current height with no initial velocity she will compress it by .148 meters. How far away from the spring is The Black Widow and what speed does she need to be moving at initially to get off the incline? Make sure to indicate what your system is and to draw energy bar charts for the different parts of The Black Widows journey. */ 183_projects/problem7a_fall2024.txt Last modified: 2025/02/24 22:43by hallstein